MARPOL Annex VI Reg 14: the sulphur cap

Background: Annex VI 1997 + 2008 MEPC.176(58) amendments

Air pollution from ships was outside the scope of the original 1973 MARPOL Convention and remained unregulated internationally until the 1997 Protocol added Annex VI as a separate annex covering air pollution and ozone-depleting substances. Adopted at an International Conference of the Parties to MARPOL convened in London in September 1997, the 1997 Protocol entered into force on 19 May 2005, eight years after adoption, once the requirement of fifteen states representing at least 50% of world merchant gross tonnage was met by Samoa’s accession on 18 May 2004.

The original 1997 text of Regulation 14 set out a global cap on sulphur in fuel oil of 4.50% m/m and a SECA cap of 1.50% m/m, with the only designated SECA at entry into force being the Baltic Sea (effective 19 May 2006, twelve months after entry into force). The 1997 cap of 4.50% m/m was deliberately set above the prevailing average sulphur content of marine residual fuel (then about 2.7% m/m globally) to capture the worst-case high-sulphur cargoes from sour crudes; only a small fraction of refineries produced fuel oil above 4.50% m/m, so the original cap acted more as a ceiling on outliers than as a structural reduction.

The Marine Environment Protection Committee adopted the 2008 amendments to Annex VI by Resolution MEPC.176(58) on 10 October 2008, with entry into force on 1 July 2010. The 2008 amendments completely rewrote Regulations 13 and 14, introduced a stepped reduction schedule for both the global and the SECA caps, established the binding 0.50% global cap from 1 January 2020 (subject to a 2018 review for feasibility), and tightened the bunker delivery note (BDN) requirements of Regulation 18. The 2008 amendments are the structural backbone of the modern Regulation 14 regime and remain in force, supplemented by Resolution MEPC.280(70) of October 2016 confirming the 2020 effective date of the 0.50% cap, Resolution MEPC.305(73) of October 2018 introducing the carriage ban for non-compliant fuel oil, and Resolution MEPC.340(77) of November 2021 revising the EGCS (scrubber) Guidelines.

The 2008 schedule for the global cap was 4.50% to 3.50% on 1 January 2012, then 3.50% to 0.50% on 1 January 2020 (the original alternative date of 1 January 2025 was rejected at MEPC 70 in 2016). The 2008 schedule for the SECA cap was 1.50% to 1.00% on 1 July 2010, then 1.00% to 0.10% on 1 January 2015. The two schedules were deliberately offset so that SECA leadership pulled the global cap down: the 0.10% SECA cap from 2015 created the demand and refinery investment that made the 0.50% global cap from 2020 logistically feasible.

The health-impact studies that motivated the 2008 amendments concluded that ship-source PM2.5 (a substantial fraction of which is secondary sulphate aerosol formed from ship-source SOx) was contributing to between 60,000 and 90,000 premature deaths per year worldwide, with disproportionate burden in port cities and coastal communities. The 2016 ICCT (International Council on Clean Transportation) and Finnish Meteorological Institute studies further estimated that the 2020 global cap would prevent approximately 150,000 premature deaths per year globally and several million asthma-related morbidity events. The cost-benefit case at MEPC 70 was overwhelming: the public-health benefit at typical valuation was estimated in the trillions of US dollars over the 2020 to 2025 period, against an industry compliance cost in the tens of billions.

Reg 14 scope: SOx + PM from any fuel combustion on a ship

Regulation 14 applies to the sulphur content of any fuel oil used on board ships. The scope is fuel-based rather than engine-based, in contrast to Regulation 13 which is engine-based. The fuel-based scope means that the same cap applies to main-propulsion engines, auxiliary engines, oil-fired boilers, oil-fired thermal-fluid heaters, gas turbines and incinerators alike: every combustion device on the ship that burns fuel oil is subject to the same sulphur cap.

Fuel oil definition

Fuel oil in Reg 14 means any fuel intended for combustion for propulsion or operation on board the ship. The definition includes residual fuel oils (HFO and the post-2020 VLSFO grades), distillate fuel oils (MGO, MDO, ULSFO), and intermediate fuel oils. The definition excludes gas fuels (LNG, LPG, methanol, ammonia, hydrogen, biogas), which are regulated under separate provisions in the IGF Code and through life-cycle GHG controls in the Net-Zero Framework. Gas-fuelled ships that also carry liquid pilot fuel are still subject to Reg 14 for the pilot-fuel portion of consumption.

Pollutants covered

Reg 14 governs both sulphur oxides (SOx) and particulate matter (PM) emissions from fuel combustion. The SOx control is direct: the sulphur in the fuel oxidises in the combustion chamber to SO2 and a small fraction of SO3, exiting in the exhaust. The PM control is indirect: a substantial fraction of marine PM, particularly the secondary sulphate aerosol formed downstream of the funnel, originates from the SOx, so the sulphur cap also delivers a PM benefit. Reg 14 does not establish a separate numerical PM limit (unlike road diesel Euro VI, which has both NOx and PM mass and number limits); the PM control is achieved by proxy through the sulphur cap.

Geographic scope

Reg 14 establishes two geographic tiers: a global cap that applies on every voyage worldwide, and a SECA cap that applies inside designated Sulphur Emission Control Areas. The transition between the two caps occurs at the SECA boundary. Outside SECA, only the global cap applies; inside SECA, the lower SECA cap applies. The transition is binary: there is no graduated transition zone. A ship crossing the SECA boundary must therefore have its fuel-supply system configured to deliver the lower-sulphur fuel before the boundary is crossed.

Combustion-device scope

Every combustion device on the ship is subject to Reg 14. This includes:

• Main-propulsion engines, both two-stroke slow-speed (typical rated speed 60 to 120 rpm) and four-stroke medium-speed (typical rated speed 400 to 900 rpm).
• Auxiliary engines, both four-stroke medium-speed and high-speed.
• Oil-fired boilers, both auxiliary and composite, used for steam generation for cargo heating, fuel-oil heating and accommodation services.
• Oil-fired thermal-fluid heaters, used on chemical and product tankers for cargo heating.
• Gas turbines, used on some LNG carriers and naval auxiliary vessels.
• Incinerators, when burning fuel oil; the sludge-burning incinerator is covered by both Reg 14 (sulphur content of the sludge if measurable) and Reg 16 (incinerator emissions standards).
• Inert-gas generators, when fuel-oil-fired; modern flue-gas IG systems on tankers use main-engine or boiler exhaust as a feedstock and are not separate combustion devices.

Emergency exception

Reg 14.6 provides a narrow emergency exception: a ship may use non-compliant fuel oil if the fuel supplied complies with Reg 14 but circumstances during the voyage prevent compliance with the lower SECA cap (typically because the ship enters a SECA earlier than planned and the compliant-fuel changeover is not completed in time). The exception requires written notification to the flag state and to the port state and is not intended for routine non-compliance.

Global sulphur cap evolution: 4.50% → 3.50% → 0.50% (IMO 2020)

The global cap on the sulphur content of fuel oil used on ships outside SECAs has evolved through three steps from 1997 to 2020.

1997 to 2011: 4.50% m/m

The original 1997 text of Reg 14 set the global cap at 4.50% m/m, effective from the entry into force of Annex VI on 19 May 2005. The 4.50% cap was a ceiling on outlier high-sulphur cargoes rather than a structural reduction: typical residual marine fuel in the 1997 to 2005 period averaged about 2.7% m/m globally, with regional variation between approximately 1.5% (Atlantic) and 3.5% (Persian Gulf, Middle East crude). The 4.50% cap acted to exclude the most extreme sour cargoes (typically from very heavy Venezuelan, Mexican Mayan or some Middle East crudes) but did not require structural change to refinery operations or to fuel supply.

2012 to 2019: 3.50% m/m

The 2008 amendments by Resolution MEPC.176(58) lowered the global cap to 3.50% m/m from 1 January 2012. The 3.50% cap was again above the prevailing global average (about 2.6% m/m by 2012, on a downward trend due to the gradual increase in the share of light sweet crudes in the global slate) but was structurally tighter than 4.50% in that it required some refineries to invest in incremental desulphurisation capacity for the highest-sulphur residual streams. The 3.50% step was relatively uneventful in implementation: bunker prices for HFO increased by about USD 5 to 10/t in the immediate aftermath as the high-sulphur tail of the supply curve was excluded.

2020 onwards: 0.50% m/m (IMO 2020)

The 2008 amendments set the global cap at 0.50% m/m from a date to be confirmed by a feasibility review. The review was conducted in 2016 by CE Delft and resulted in the Resolution MEPC.280(70) of October 2016, confirming 1 January 2020 as the effective date of the 0.50% cap. The 0.50% step was structurally transformative: it required the bunker market to shift from approximately 80% HFO at about 2.6% sulphur to a fundamentally new product mix. The transition is the regulatory event known as IMO 2020.

The pre-cap fears of widespread fuel shortages, refinery blending failures, fuel-incompatibility incidents and price spikes mostly did not materialise. The bunker industry produced sufficient VLSFO (very-low-sulphur fuel oil) in time, refineries had invested in residual-desulphurisation capacity through 2018 and 2019, and the transition from HFO to VLSFO was largely completed in the December 2019 to February 2020 window. Initial fuel-quality problems (incompatibility between different VLSFO blends, sediment formation, cat-fines) were managed through tighter ISO 8217 quality requirements and bunker-vetting practices. The price premium of VLSFO over HFO was about USD 200 to 300/t in the first year (2020) and stabilised at about USD 100 to 200/t from 2021 onwards.

The mathematical structure of the global-cap evolution is:

The corresponding SOx emission factor is approximately 20 kg SO2 per tonne of fuel per percent sulphur, derived from the molecular-mass ratio (one tonne of S in fuel forms 64/32 = 2 tonnes of SO2; 1% S in fuel therefore forms 0.02 tonnes or 20 kg of SO2 per tonne of fuel burnt). At 3.50% S in 2019, a typical post-Panamax container ship burning 200 tonnes of HFO per day was emitting 14 tonnes of SO2 per day. At 0.50% S in 2020, the same ship burning the same VLSFO mass emitted 2 tonnes of SO2 per day, an 86% reduction. The aggregate global reduction in ship-source SOx in 2020 was approximately 8 to 10 million tonnes of SO2 per year, against a pre-cap baseline of about 11 million tonnes per year.

Future steps

There is no current proposal to reduce the global cap below 0.50% m/m in the IMO. The IMO Net-Zero Framework, approved at MEPC 83 in April 2025 and under formal adoption procedures as of 2026 (MEPC/ES.2 in October 2025 adjourned without adoption; resumed negotiation 2026), introduces life-cycle GHG-intensity targets in grams of CO2-equivalent per megajoule but does not establish further SOx targets. The 0.50% global cap is therefore expected to remain in force indefinitely, with future tightening to occur via expansion of SECA designations rather than further global reductions.

SECA cap evolution: 1.50% → 1.00% → 0.10% (since 2015)

The SECA cap has evolved through three steps from 1997 to 2015, mirroring but offset from the global-cap trajectory.

Pre-2010: 1.50% m/m

The original 1997 text set the SECA cap at 1.50% m/m, effective from the date of entry into force of each SECA designation. The Baltic Sea SECA, the only designated SECA in 1997, applied 1.50% from 19 May 2006. The North Sea SECA applied 1.50% from 22 November 2007. The 1.50% cap was substantially below the prevailing HFO average (about 2.7% m/m globally in 2006) but was achievable through a combination of low-sulphur HFO blends from sweet-crude refineries and modest distillate-fuel use.

2010 to 2014: 1.00% m/m

The 2008 amendments lowered the SECA cap to 1.00% m/m from 1 July 2010. The 1.00% step required a meaningful shift in the SECA bunker market from generic low-sulphur HFO to dedicated SECA-grade product. The transition was implemented without widespread disruption; SECA-grade fuel premiums of about USD 30 to 60/t emerged in the 2010 to 2014 period.

2015 onwards: 0.10% m/m

The 2008 amendments set the SECA cap at 0.10% m/m from 1 January 2015, the headline regulatory event known in the industry as MARPOL 2015 or the 0.10% SECA cap. The 0.10% cap is structurally distillate-grade: a fuel of 0.10% sulphur is essentially MGO (DMA grade under ISO 8217) or a heavily desulphurised distillate equivalent (ULSFO). Residual-fuel blending to achieve 0.10% is technically feasible but uneconomic at scale. The 2015 transition therefore shifted SECA fuel consumption from HFO blends to dedicated MGO supply, with associated price premiums of USD 200 to 400/t over global HFO at the time.

The mathematical structure of the SECA-cap evolution is:

SECA fuel-availability transition

Pre-2015 fears of MGO shortage in the Baltic and North Sea SECAs were largely unfounded. European refineries had distillate spare capacity (the European product slate is distillate-heavy due to road-diesel demand) and could redirect a fraction of distillate output to marine bunkers without disrupting the road-diesel market. The 2015 transition was implemented smoothly, with fuel-quality problems concentrated on cold-flow issues (MGO has a higher cloud point and pour point than HFO blends and can wax in cold North Sea bunker tanks, requiring tank heating or kerosene blending in winter).

SECA versus global-cap relationship

Since 1 January 2020, the global cap has been 0.50% and the SECA cap has been 0.10%. The SECA cap remains five times lower than the global cap, preserving the original SECA-leadership rationale: SECAs are progressive, dragging the global market downward. The next round of SECA cap reductions, if any, would occur via designation of additional SECAs at a hypothetical lower limit (the IMO has not adopted any cap below 0.10% in any designated SECA, and there is no current proposal to do so).

Baltic SECA (MEPC.116(51) 2006, 0.10% from 2015)

The Baltic Sea SECA was the first SECA designated under Annex VI, designated by the original 1997 text and brought into operational force on 19 May 2006, twelve months after the entry into force of Annex VI. The Baltic SECA is administered jointly with the existing Helsinki Commission (HELCOM) regional regime under the Helsinki Convention 1992, which provides the regional governance and the marine-monitoring infrastructure.

The Baltic SECA covers the Baltic Sea, the Gulf of Bothnia, the Gulf of Finland and the entrance to the Baltic Sea bounded by the parallel of the Skaw in the Skagerrak at 57°44.8’N. The SECA includes the EEZ and territorial waters of all nine HELCOM coastal states: Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia and Sweden. The SECA boundary at 57°44.8’N runs roughly across the Skagerrak from Skagen (Denmark) to the Norwegian coast, joining the North Sea SECA boundary to its west.

The Baltic SECA applied the 1.50% cap from 19 May 2006, the 1.00% cap from 1 July 2010 and the 0.10% cap from 1 January 2015. The Baltic was also subsequently designated as a NECA under Resolution MEPC.286(71) of 7 July 2017, with Tier III NOx applying from 1 January 2021 (see Regulation 13 and the Baltic SECA + NECA wiki page). The Baltic is therefore a joint SECA + NECA as of 2026.

Compliance in the Baltic SECA is enforced jointly by the nine HELCOM coastal states under the Paris MoU memorandum-of-understanding framework. Port-state inspections at Baltic ports (Copenhagen, Helsinki, Tallinn, Riga, Klaipeda, Gdansk, Stockholm, Saint Petersburg) include sulphur sampling under the THETIS-EU electronic inspection database. The Baltic SECA has the highest sulphur-compliance rate of any SECA, typically above 99% in routine inspections by 2024.

The HELCOM Maritime Working Group also operates air-monitoring sniffer stations at fixed coastal positions and on aircraft for periodic enforcement-flying campaigns. Sniffer stations measure SO2 and CO2 in plumes downwind of passing ships, computing the fuel sulphur ratio as the ratio of SO2 to CO2 (the SO2:CO2 ratio in the exhaust is a direct function of fuel-sulphur content for known carbon content of the fuel). A sniffer-detected non-compliance triggers a follow-up inspection at the next port of call.

North Sea SECA (MEPC.117(52) 2007, 0.10% from 2015)

The North Sea SECA was the second SECA designated under Annex VI, designated by Resolution MEPC.117(52) of 15 October 2004 and brought into operational force on 22 November 2007. The North Sea SECA covers the North Sea, the English Channel and the eastern Atlantic approaches, bounded by the parallel of 62°N (the Norway-Faroes line) to the north, the parallel of 48°27’N (the Brest-Lizard line) to the south, the meridian of 5°W (the Shetland-Faroes line) to the west, and the eastern coast of the United Kingdom and the western coast of Norway, Denmark, the Netherlands, Belgium, France and Germany.

The North Sea SECA applied the 1.50% cap from 22 November 2007, the 1.00% cap from 1 July 2010 and the 0.10% cap from 1 January 2015. The North Sea was also subsequently designated as a NECA under Resolution MEPC.286(71) of 7 July 2017, with Tier III NOx applying from 1 January 2021. The North Sea is therefore a joint SECA + NECA as of 2026 (see the North Sea SECA + NECA wiki page).

The North Sea SECA carries the highest density of cargo traffic in the world: approximately 30% of global container TEU passes through North Sea ports (Rotterdam, Antwerp-Bruges, Hamburg, Felixstowe, Le Havre, Bremerhaven), and the SECA includes the major bunker hub of Rotterdam (the second-largest bunker port worldwide after Singapore). Compliance enforcement is correspondingly intensive, with the Paris MoU secretariat coordinating port-state inspections across the SECA states.

The Belgian Royal Institute for Natural Sciences operates a fixed sniffer station on the Wandelaar offshore platform off Zeebrugge, monitoring all ships transiting the southern North Sea. The Dutch Human Environment and Transport Inspectorate (ILT) operates aerial sniffer flights from Lelystad. The German Federal Maritime and Hydrographic Agency (BSH) operates fixed sniffers at Wedel on the Elbe approach to Hamburg. These three monitoring nodes together cover most of the high-density traffic in the North Sea SECA.

The non-compliance rate in the North Sea SECA, measured by sniffer-detected events followed up by sampling, was about 5% in 2015 (the first year of the 0.10% cap), declining to about 3% in 2018, 2% in 2020 (even with the IMO 2020 distraction) and about 1% in 2024. The detection rate for genuine non-compliance versus sample-error false positives is well above 0.95, reflecting the maturity of the sniffer methodology.

North American SECA (MEPC.190(60) 2012, joint with NECA)

The North American SECA was the third SECA designated under Annex VI, designated by Resolution MEPC.190(60) of 26 March 2010 and brought into operational force on 1 August 2012. The North American SECA covers the Atlantic, Pacific and Gulf of Mexico waters within 200 nautical miles of the baselines of the United States (excluding Alaska south of 60°N), Canada (Atlantic and Pacific provinces) and France (Saint Pierre and Miquelon). The SECA boundary follows the 200 NM contour with detailed waypoints listed in Appendix VII of Annex VI.

The North American SECA was the first joint SECA + NECA designation: Resolution MEPC.190(60) covered both Reg 14 sulphur and Reg 13 Tier III NOx in a single instrument. The SECA cap was 1.00% from 1 August 2012, then 0.10% from 1 January 2015. The NECA Tier III applied from 1 January 2016 for engines installed on ships with a keel-laying date on or after that date (see the North American ECA wiki page).

The North American SECA is enforced by the US Coast Guard (USCG) and Environmental Protection Agency (EPA) jointly in US waters, by Transport Canada in Canadian waters and by the French Maritime Affairs in Saint Pierre and Miquelon waters. Enforcement at major US ports (New York/New Jersey, Los Angeles/Long Beach, Houston, Savannah, Charleston, Seattle/Tacoma) includes EPA portable XRF sampling at the dock. Canadian enforcement at Vancouver, Halifax and Montreal includes Transport Canada port-state inspections under the Tokyo MoU regional framework.

The North American SECA has a unique technical feature: a continuous-monitoring requirement under EPA Part 1043 for ships using EGCS (scrubbers). Scrubber-equipped ships transiting the SECA must record continuous wash-water and exhaust monitoring data and produce the records on demand; this requirement is more prescriptive than the IMO MEPC.184(59) baseline.

US Caribbean SECA (MEPC.202(62) 2014, joint with NECA)

The US Caribbean SECA was the fourth SECA designated under Annex VI, designated by Resolution MEPC.202(62) of 15 July 2011 and brought into operational force on 1 January 2014. The US Caribbean SECA covers the waters within 50 to 200 nautical miles (depending on segment) of the baselines of Puerto Rico and the US Virgin Islands. The SECA boundary follows a polygon defined in Appendix VII of Annex VI, with the principal cargo destinations of San Juan and Charlotte Amalie within the SECA.

The US Caribbean SECA was the second joint SECA + NECA designation: Resolution MEPC.202(62) covered both Reg 14 sulphur and Reg 13 Tier III NOx in a single instrument. The SECA cap was 1.00% from 1 January 2014, then 0.10% from 1 January 2015. The NECA Tier III applied from 1 January 2016 for engines installed on ships with a keel-laying date on or after that date (see the US Caribbean ECA wiki page).

The US Caribbean SECA is enforced jointly by the USCG and EPA in the same regulatory architecture as the North American SECA, with the same Part 1043 continuous-monitoring requirement for scrubber-equipped ships. The traffic volume is substantially lower than the North American SECA (approximately one-tenth) but includes high-density cruise-ship operation at San Juan and Charlotte Amalie, which made the SECA designation politically and environmentally important.

The US Caribbean SECA does not extend beyond the US waters into the wider Caribbean. The independent Caribbean states of Jamaica, Dominican Republic, Cuba, Bahamas, Trinidad and Tobago and the CARICOM Eastern Caribbean (Antigua, Barbados, Saint Lucia, Saint Vincent, Grenada) have not jointly applied for SECA extension. Discussions of a wider Caribbean SECA at the CARICOM Council of Ministers in 2023 and 2024 have not produced a formal IMO submission as of 2026.

Mediterranean SECA (MEPC.361(79) December 2022, effective 1 May 2025)

The Mediterranean SECA is the fifth SECA designated under Annex VI, designated by Resolution MEPC.361(79) adopted on 16 December 2022 at MEPC 79 and brought into operational force on 1 May 2025. The amendments entered into force on 1 May 2024 (the standard 16-month lead), with the 0.10% sulphur limit applying from 1 May 2025. The Mediterranean SECA covers the entire Mediterranean Sea, including the Sea of Marmara via the Dardanelles, but excluding the Black Sea (the boundary at the Bosphorus Strait runs at 41°00’N north of Istanbul).

The Mediterranean SECA is the first regional SECA designated by a regional grouping of states under the Barcelona Convention framework. The proposal originated in the 2018 Barcelona Convention Ministerial Declaration, was developed by REMPEC (the Regional Marine Pollution Emergency Response Centre for the Mediterranean Sea) and the IMO Secretariat from 2019 to 2022, and was adopted by MEPC 79 in December 2022. The 22 Mediterranean coastal states (Spain, France, Italy, Greece, Cyprus, Malta, Slovenia, Croatia, Bosnia-Herzegovina, Montenegro, Albania, Turkey, Syria, Lebanon, Israel, Egypt, Libya, Tunisia, Algeria, Morocco, plus the British Overseas Territory of Gibraltar and the European Union as a regional integration organisation) are joint co-sponsors of the SECA.

The Mediterranean SECA applies the 0.10% cap from 1 May 2025 directly, without a transitional 1.00% phase. This is the first SECA to apply the 0.10% cap immediately at designation, reflecting the maturity of low-sulphur fuel supply by 2025 and the absence of the transition pressures that motivated the 2010 to 2015 stepped reduction. The Mediterranean is not yet a NECA: the SECA designation is sulphur-only as of 2026. NECA designation is under negotiation under the Barcelona Convention 2024 ministerial declaration, with a likely effective date of 1 January 2030 or 2031 (see the Mediterranean SECA 2025 wiki page).

The Mediterranean SECA covers approximately 20% of global cargo TEU (the Suez-Mediterranean trunk route plus intra-Mediterranean short-sea trades), and its designation is the largest single increment in SECA-covered traffic since the original Baltic and North Sea designations. The estimated air-quality benefit is approximately 0.5 to 0.8 million tonnes per year of SO2 reduction in the Mediterranean basin, with corresponding PM2.5 reduction of approximately 50,000 tonnes per year and an estimated avoidance of 1,100 premature deaths per year.

Implementation as of 2026 has been broadly successful: bunker supply at Mediterranean ports (Algeciras, Gibraltar, Malta, Piraeus, Genoa, Marseille, Barcelona, Limassol, Ceuta, Suez Port Said) shifted to 0.10% MGO and ULSFO products by Q1 2025, and port-state inspection rates in the first six months (May to October 2025) showed a non-compliance rate of approximately 4 to 6%, declining to about 2 to 3% by Q1 2026 as the market settled.

Canadian Arctic SECA proposal (under negotiation 2026)

A Canadian Arctic SECA is under negotiation as of 2026, having been the subject of a 2023 Canadian submission to MEPC 80 and a follow-up working-group session at MEPC 82 in October 2025. The proposal would cover the Canadian Arctic waters north of 60°N, including the Northwest Passage, Hudson Bay, Hudson Strait, Foxe Basin and the Beaufort Sea. The estimated effective date is 1 January 2028 or 2029, subject to MEPC adoption in 2026 or 2027 and the standard sixteen-month implementation lead.

The Canadian Arctic SECA proposal is motivated by Arctic black carbon concerns: black carbon (a component of PM emitted by ship combustion) deposited on Arctic snow and ice has a strong albedo-warming effect, accelerating ice melt. The 0.10% sulphur cap reduces secondary sulphate aerosol but does not directly reduce black carbon; the SECA proposal therefore envisages additional black-carbon controls (typically through an indirect requirement that distillate fuels with low aromatic content be used, since aromatic-rich residual fuels produce more black carbon).

The proposal is supported by the Polar Code 2017 framework and by the Arctic Council, with active sponsorship from Canada and observer support from Denmark (Greenland), Norway, the United States (Alaska) and Russia. The principal blocker as of 2026 is the absence of a separately designated Canadian Arctic NECA: the proposal as currently drafted is sulphur-only, but the technical case for joint sulphur and NOx designation in the Arctic is strong, and a working-group recommendation at MEPC 84 may extend the proposal to a joint SECA + NECA.

A separate Norwegian Sea SECA proposal, contemplated since 2019, is under preliminary study by Norway as of 2026 and has not yet been submitted to IMO. The Norwegian proposal would extend the existing North Sea SECA up the Norwegian coast to the Russian border and would close a regulatory gap along the Norwegian coast where heavy-traffic fishing-vessel and offshore-supply operations currently fall outside any SECA.

IMO 2020 carriage ban under MEPC.305(73)

The carriage ban under Resolution MEPC.305(73) of October 2018, effective 1 March 2020, prohibits a ship from carrying non-compliant fuel oil for use on board, except where the ship is fitted with an approved exhaust gas cleaning system (scrubber). The carriage ban is the enforcement teeth of the IMO 2020 sulphur cap.

Rationale

Without a carriage ban, a ship could:

• Bunker high-sulphur fuel at one port, claim it was loaded but not used, and then in fact use it during a voyage with no on-board evidence of the use.
• Plead an emergency exception (Reg 14.6) to use non-compliant fuel without external verification.
• Evade detection by switching to compliant fuel only when port-state inspection was anticipated.

The carriage ban closes these loopholes: if a ship without a scrubber is found to have non-compliant fuel oil on board, the ship is non-compliant regardless of whether the fuel was actually being used.

Effective date

The carriage ban became effective 1 March 2020, two months after the cap itself entered force on 1 January 2020. The two-month window allowed ships to consume residual high-sulphur fuel inventories purchased before 1 January 2020. After 1 March 2020, all on-board fuel oil must be either compliant (≤0.50% globally, ≤0.10% in SECA) or designated for use only in conjunction with a scrubber.

Scrubber exception

Ships fitted with an approved scrubber may carry high-sulphur fuel oil (HSFO) above 0.50% on board for use through the scrubber. The scrubber-equipped ship must:

• Hold an EGCS Approval Certificate from the flag administration.
• Comply with the EGCS Guidelines (MEPC.184(59) or MEPC.340(77)).
• Operate the scrubber whenever HSFO is being used.
• Maintain wash-water and exhaust monitoring records.
• Demonstrate that the SOx-to-CO2 ratio in the exhaust is at or below the equivalent compliant-fuel ratio.

Carriage-ban inspection

PSC inspections under the carriage-ban regime examine the ship’s fuel-storage tanks and service tanks for any non-compliant fuel. Tank sampling is allowed and is the typical practice for ships suspected of non-compliance. The carriage ban has been the principal enforcement instrument since 1 March 2020 and has driven the 5% non-compliance rate in 2020 down to about 1% by 2024.

Operational consequences

The carriage ban means a ship that bunkers HSFO must either (a) install a scrubber before bunker, or (b) consume the HSFO before the carriage-ban deadline (no longer feasible after 1 March 2020). For a non-scrubber ship, the only legal option is to bunker only compliant fuel from 1 March 2020 onwards. The carriage ban effectively eliminated the residual HFO market for non-scrubber ships globally and forced the structural shift to VLSFO and MGO that defined the post-2020 marine bunker landscape.

Alternative compliance: VLSFO + ULSFO + MGO

The most common compliance pathway under Reg 14 is compliant low-sulphur fuel oil, which comes in three principal grades distinguished by sulphur content and physical properties.

VLSFO (Very Low Sulphur Fuel Oil) for global cap compliance

VLSFO is residual or hybrid fuel oil with sulphur content at or below 0.50% m/m. VLSFO emerged as a dedicated bunker product in 2019 (pre-cap) and dominated the global bunker market from 2020 onwards. VLSFO is typically produced by:

• Hydrodesulphurisation (HDS) of vacuum gas oil (VGO) combined with low-sulphur residual streams from sweet-crude refining.
• Blending of low-sulphur residual streams (from West African or North Sea sweet crudes) with hydrocracked VGO.
• Direct production at modern hydrocrackers and residue desulphurisers, particularly the post-2018 generation in Saudi Arabia, the UAE, India and South Korea.

VLSFO physical properties are highly variable between blends, with viscosity ranging from 50 cSt to 380 cSt at 50°C, density from 0.93 to 0.99 kg/L, pour point from −5 to +30°C, and aromatic content from 30 to 70%. The variability has caused operational problems, particularly incompatibility between different VLSFO blends (mixing blends from different sources can cause asphaltene precipitation and engine fuel-pump damage). The 2017 ISO 8217 standard introduced a formal stability test (ISO 10307-2 total sediment potential) for VLSFO, and bunker-vetting practice now mandates compatibility checks before bunker-mixing.

ULSFO (Ultra Low Sulphur Fuel Oil) for SECA compliance

ULSFO is residual or hybrid fuel oil with sulphur content at or below 0.10% m/m. ULSFO is used in SECAs as an alternative to MGO for ships that prefer to keep their fuel system on residual-grade product (ULSFO has the higher viscosity of HFO and runs in unmodified HFO fuel pumps and injectors, while MGO requires fuel-pump modification or fuel-cooling for some applications). ULSFO is typically produced by deeper hydrodesulphurisation than VLSFO, often combined with kerosene blending.

MGO (Marine Gas Oil, DMA grade) for SECA compliance and global cap

MGO is distillate fuel oil with sulphur content at or below 0.10% m/m, equivalent to road-diesel sulphur content (which is 10 ppm or 0.001% m/m in the EU and US, slightly tighter than MGO). MGO is the dominant SECA-grade fuel for ships not equipped with scrubbers, and many ships use MGO globally (not just in SECA) for operational simplicity (single fuel grade, no changeover required at SECA boundary, full DSGen and lifeboat-engine compatibility).

The MGO grades under ISO 8217:2017 are DMX, DMA, DMZ, DMB, with progressively higher viscosity and density. The most common SECA bunker is DMA grade (0.10% S maximum, viscosity 1.5 to 6.0 cSt at 40°C, flash point ≥60°C). The premium of MGO over HFO is typically USD 200 to 400/t, reflecting both the desulphurisation cost and the distillate-supply cost.

Fuel changeover at SECA boundary

Ships not equipped with scrubbers and using both VLSFO (outside SECA) and MGO (inside SECA) must execute a fuel changeover before the SECA boundary. The changeover involves:

• Stopping the VLSFO supply to the engines and boilers.
• Flushing the fuel-pump suction lines and service tanks with MGO.
• Bringing all fuel-consuming devices on the ship onto MGO.
• Recording the changeover in the Oil Record Book with the position, date and time.

The changeover takes typically 30 to 90 minutes, depending on the system architecture and the volume of HFO in the lines and tanks. Ships planning changeover at the SECA boundary must begin the changeover at least one hour before the boundary to allow for full purge.

Per-fuel emissions reference

The cross-link page per-fuel WTW VLSFO/MGO compares the well-to-wake emission profiles of VLSFO and MGO against HFO and LNG on a CO2-equivalent basis under the IMO LCA Guidelines.

Alternative compliance: scrubber (EGCS) systems

The second compliance pathway under Reg 14 is the Exhaust Gas Cleaning System (EGCS), commonly known as a scrubber. The scrubber installs in the exhaust gas path between the engine or boiler and the funnel, washing the SO2 out of the exhaust gas with seawater or treated freshwater before the gas is released to atmosphere.

Scrubber thermodynamics

The scrubber operates on the chemical reaction between SO2 and water:

The reaction is rapid and substantially complete in a wet scrubber with adequate water-to-exhaust ratio (typically 30 to 50 m³ wash water per MWh of engine power). The reaction is acid-neutral if the wash water is alkaline (seawater is mildly alkaline at pH 8.0 to 8.2, and the buffering capacity of seawater is sufficient to neutralise the acid for typical scrubber operation).

Scrubber removal efficiency

A typical wet scrubber achieves 97 to 99% SO2 removal when operating on HSFO, reducing the exhaust SO2-to-CO2 ratio to a level equivalent to or below 0.10% sulphur compliant fuel. The MEPC.184(59) Guidelines define the SO2 / CO2 ratio limit for compliance:

• For a fuel of 0.10% S (SECA-equivalent), the SO2/CO2 mass ratio limit is 4.3 ppm by volume or equivalent.
• For a fuel of 0.50% S (global-cap equivalent), the SO2/CO2 mass ratio limit is 21.7 ppm.
• For a fuel of 1.00% S, the limit is 43.3 ppm.
• For a fuel of 1.50% S, the limit is 65.0 ppm.
• For a fuel of 4.50% S, the limit is 195.0 ppm.

A scrubber operating on 3.50% S HSFO must therefore achieve at least 21.7 / 151.7 = 86% removal to meet the 0.50% global-cap-equivalent ratio, or 4.3 / 151.7 = 97% removal to meet the 0.10% SECA-equivalent ratio. Modern scrubbers comfortably achieve both.

Scrubber installation cost

Scrubber retrofit cost on a typical post-Panamax container ship is approximately USD 4 to 8 million (2020 to 2024 range), including the scrubber tower, the wash-water pumps, the wash-water treatment system, the seawater intake and discharge, the funnel modifications and the dry-dock time. The retrofit takes typically 30 to 60 days of dry-dock and may be combined with scheduled five-year special-survey docking to amortise the off-hire cost.

Scrubber operating cost

Scrubber operating cost includes:

• Pumping power: typically 1 to 2% of engine power, drawn from the auxiliary engines (50 to 200 kW for a typical container ship).
• Maintenance: typically USD 100,000 to 300,000 per year, including spray-nozzle replacement, packing-bed inspection, instrument calibration.
• Wash-water treatment: for closed-loop systems, the caustic (NaOH) consumption is typically 30 to 50 kg per tonne of HSFO burnt, at a cost of approximately USD 15 to 30 per tonne of fuel.

Scrubber payback economics

The scrubber business case rests on the VLSFO-to-HFO price spread: a scrubber-equipped ship continues to bunker cheap HSFO instead of expensive VLSFO. The payback period is approximately:

For a typical VLCC tanker burning 30,000 t/year, a price spread of USD 150/t and a scrubber cost of USD 5 million with USD 200,000/year operating cost:

For a typical post-Panamax container ship burning 20,000 t/year at the same spread:

Typical industry payback periods of 1 to 3 years made the scrubber retrofit attractive in the 2020 to 2022 window. Approximately 5,000 ships globally had been fitted with scrubbers by 2024, representing about 25% of global bunker fuel demand by mass.

Open-loop vs closed-loop vs hybrid scrubber

Three scrubber architectures are used at sea, distinguished by the wash-water management.

Open-loop scrubber

The open-loop scrubber uses seawater drawn from a sea chest as the wash-water medium. The seawater absorbs the SO2 and is discharged overboard after wash-water treatment. The open-loop system relies on the natural alkalinity of seawater (pH 8.0 to 8.2) to neutralise the absorbed acid; no chemical addition is required.

Open-loop is the simplest, cheapest and most common scrubber architecture, accounting for approximately 75% of the global scrubber-equipped fleet as of 2024. Capital cost is typically USD 4 to 6 million for a post-Panamax container ship.

The open-loop architecture is not suitable in low-alkalinity waters (Baltic Sea brackish areas, some river estuaries, fresh-water lakes) where the buffering capacity is insufficient to neutralise the acid. The architecture is also subject to port-state restrictions on wash-water discharge (see the next section).

Closed-loop scrubber

The closed-loop scrubber uses fresh water dosed with sodium hydroxide (NaOH, caustic soda) as the wash-water medium. The wash water circulates in a closed loop with periodic bleed of saturated water to a sludge tank for shore disposal, and periodic make-up of fresh water and caustic.

Closed-loop is suitable in any water (including fresh water and very low-alkalinity waters) and produces no overboard discharge during normal operation. Capital cost is higher than open-loop (typically USD 6 to 8 million for a post-Panamax container ship) due to the freshwater treatment loop, the caustic dosing system and the sludge storage tanks. Operating cost is also higher due to the caustic consumption (typically USD 15 to 30 per tonne of HFO burnt) and the sludge disposal cost (typically USD 50 to 100 per cubic metre at port shore reception).

Closed-loop accounts for approximately 5% of the global scrubber-equipped fleet as of 2024. The architecture is typically chosen for ships trading principally in port-state-restricted waters or in low-alkalinity zones.

Hybrid scrubber

The hybrid scrubber combines the open-loop and closed-loop architectures in a single unit, switching between modes depending on the operational situation. The hybrid runs in open-loop mode at sea in normal alkalinity waters (cheap operation, no caustic) and in closed-loop mode in port or in low-alkalinity waters (no overboard discharge).

Hybrid is the most flexible architecture but the most expensive (typically USD 7 to 10 million capital cost for a post-Panamax container ship). Hybrid accounts for approximately 20% of the global scrubber-equipped fleet as of 2024 and is the typical choice for ships trading in mixed open-loop and closed-loop port-state regimes (for example, a ship trading between Singapore (open-loop banned in port) and Rotterdam (open-loop permitted)).

Dry scrubber (limited deployment)

A small fraction (<1%) of installed scrubbers are dry scrubbers, using a calcium-hydroxide pellet bed instead of liquid water. Dry scrubbers consume calcium-hydroxide pellets (typically 10 to 30 kg per tonne of HFO) and produce calcium-sulphate ash for shore disposal. Dry scrubbers are less common at sea due to the storage volume of the pellet bed and the disposal logistics for the ash, but are technically interesting for low-alkalinity-water ships and for niche applications such as deep-sea fishing-vessel auxiliary boilers.

Scrubber Guidelines: MEPC.184(59) 2009 + MEPC.340(77) 2021 revision

The IMO has adopted two generations of EGCS Guidelines.

MEPC.184(59) of 2009: original Guidelines

Resolution MEPC.184(59) of 17 July 2009, the 2009 EGCS Guidelines, established the original scrubber type-approval, certification, on-board verification and wash-water criteria. The 2009 Guidelines contain:

• Scheme A: type-approval of the scrubber unit, with on-board operational compliance verified by the SO2/CO2 ratio measurement. Scheme A is the dominant pathway, used by approximately 95% of installed scrubbers.
• Scheme B: continuous on-board emission monitoring without unit type-approval. Scheme B is used in some niche applications.
• Wash-water discharge criteria for open-loop and hybrid scrubbers in open-loop mode: pH ≥6.5 measured at the discharge port (corrected for the natural pH at the inlet), PAH ≤50 µg/L (15-minute mean, normalised to 45 t/MWh wash water flow), turbidity ≤25 FNU above the inlet (15-minute mean), nitrate concentration <60 mg/L.
• Sludge handling for closed-loop and hybrid scrubbers in closed-loop mode: sludge must be retained on board and discharged only at port reception facilities.
• EGCS Approval Certificate issued by the flag administration upon successful type-approval and on-board commissioning.
• EGCS Record Book documenting operating hours, fuel consumed, wash-water parameters and any non-compliance events.

MEPC.340(77) of 2021: revised Guidelines

Resolution MEPC.340(77) of November 2021, the 2021 revised EGCS Guidelines, updated the original Guidelines to reflect the experience of the IMO 2020 transition and the growth of the scrubber fleet. The 2021 revision includes:

• Tightened wash-water criteria: pH limit clarified to 6.5 absolute or with a smaller correction relative to inlet; PAH measurement methodology clarified; nitrate measurement extended.
• Emission monitoring redundancy: requirement for two independent SO2/CO2 measurement instruments with cross-check logic, replacing the single-instrument provision of the 2009 Guidelines.
• Wash-water sampling and reporting requirements for periodic wash-water samples to the flag administration.
• Type-approval scope clarified: the type-approval covers a specific engine-scrubber-fuel combination, and changes to engine type or rated power require re-type-approval.
• End-of-life management: provisions for scrubber decommissioning, including the disposal of the scrubber tower internals (which contain accumulated sulphate and PAH residues).

MEPC 78 (June 2022) supplementary guidance circulars

MEPC 78 in June 2022 approved two supplementary guidance circulars that sit alongside the MEPC.340(77) revised Guidelines:

• MEPC.1/Circ.899: Draft guidelines for risk and impact assessment of the discharge water from exhaust gas cleaning systems. The circular provides a methodology for port states and flag states to assess the environmental risk of open-loop EGCS discharge at individual locations, taking account of the local hydrodynamic conditions, the baseline water quality and the cumulative load from the traffic density at anchor or at berth. The methodology supports port states in deciding whether to impose local open-loop discharge bans on a scientific, site-specific basis rather than a blanket precautionary prohibition.

• MEPC.1/Circ.900: Guidance regarding the delivery of EGCS residues and stored discharge water to port reception facilities. The circular clarifies that closed-loop bleed water and sludge must be delivered to port reception under MARPOL Annex VI, and that ports are expected to provide adequate reception capacity. MEPC.1/Circ.900 defines “residues” to include scrubber sludge (the accumulated particulate concentrate from the closed loop) and bleed water (the periodic purge from the recirculation system), distinguishing them from the continuous overboard discharge of an open-loop system.

MEPC 83 in April 2025 noted a submission calling for mandatory controls on EGCS discharge water under MARPOL and forwarded it to the PPR Sub-Committee (PPR 13 in early 2026) for further consideration. The ongoing PPR work may produce a future binding instrument tightening or superseding the MEPC.1/Circ.899 risk-assessment approach.

Class-society type-approval

Type-approval of scrubber units is conducted by IACS class societies under flag-administration delegation. The principal class type-approval programmes are at DNV (the largest by market share), Lloyd’s Register, ABS, Bureau Veritas, NK (ClassNK), RINA, KR (Korean Register), CCS (China Classification Society), RS (Russian Maritime Register) and IRS (Indian Register). Each class operates a type-approval programme on common IACS lines, and a unit type-approved by one class is generally accepted by other classes for installation on ships of any flag.

The principal scrubber manufacturers as of 2026 are Wartsila (formerly Hamworthy and Krystallon, market leader by installed base), Yara Marine Technologies, Alfa Laval PureSOx, Clean Marine Solutions, Damen Green Solutions and several Chinese manufacturers (Yantai Damon, Sunrui marine). The industry is consolidated around 6 to 8 principal vendors with mature product lines.

Wash-water criteria: pH ≥6.5, PAH ≤50 µg/L, turbidity 25 FNU

The wash-water discharge criteria for open-loop and hybrid scrubbers (in open-loop mode) under MEPC.184(59) and MEPC.340(77) are the principal numerical limits in the EGCS Guidelines.

pH limit

The wash-water discharge pH must be at or above 6.5, measured at the discharge port. The limit may be applied:

• As an absolute pH ≥6.5 at the discharge port, or
• As a delta pH relative to the inlet pH, with the discharge plume diffused to within a defined distance from the hull such that the at-sea pH is restored to natural background within a short distance.

The pH limit is the most binding wash-water criterion in practice. A scrubber operating at full power on HSFO produces a wash-water discharge with pH typically 3.0 to 4.5 at the discharge port (highly acidic), which then mixes with seawater to reach pH ≥6.5 within typically 0.5 to 2 metres from the hull. The compliance demonstration involves a CFD or physical-model study during type-approval.

PAH limit

The wash-water PAH (polycyclic aromatic hydrocarbon) concentration must be at or below 50 µg/L as a 15-minute mean, normalised to 45 m³/MWh wash-water flow rate (a higher flow rate dilutes the PAH and is therefore credited; a lower flow rate concentrates the PAH and is debited). The PAH originates from incomplete combustion in the engine and is captured in the scrubber along with the SO2.

The PAH limit is technically straightforward to meet on modern engines (HSFO combustion at high load produces typically 5 to 20 µg/L PAH in scrubber wash water, well below 50 µg/L). The limit can be exceeded at very low engine load with cold combustion (low-load PAH can spike to 30 to 80 µg/L), and the compliance pathway is to operate the scrubber in closed-loop mode at low load (the closed-loop sludge captures the PAH and discharges to port reception).

Turbidity limit

The wash-water turbidity must be at or below 25 FNU (Formazin Nephelometric Units) above the inlet turbidity, measured as a 15-minute mean. The turbidity originates from soot, ash and coke fragments captured in the scrubber. The limit is straightforward to meet (typical turbidity is 5 to 15 FNU above inlet).

Nitrate limit

The 2021 revised Guidelines added a nitrate concentration limit of 60 mg/L in the wash-water discharge. The nitrate originates from absorbed NOx in the scrubber (a small fraction of NO2 absorbs into the wash water as nitric acid). The limit is binding for high-NOx engines (Tier I or pre-Tier engines) and is straightforward for Tier II and Tier III engines.

Other parameters

Additional parameters monitored continuously and recorded in the EGCS Record Book are:

• Wash-water flow rate (m³/h or m³/MWh).
• Discharge temperature (typically 35 to 45°C, no numerical limit but recorded).
• SO2/CO2 ratio in exhaust (the principal compliance metric, recorded continuously).
• Engine load (from engine telegraph or shaft torque).
• Fuel consumption and fuel sulphur content (cross-checked against BDN under Reg 18).

Port-state bans on open-loop scrubber discharge: Singapore, China, UAE, Oman

A growing list of port states has imposed bans on open-loop scrubber wash-water discharge in their port waters, even where the discharge complies with the IMO MEPC.184(59) criteria. These bans are based on local water-quality concerns, particularly the cumulative effect of multiple scrubber discharges in confined port waters, the local PAH burden in semi-enclosed harbours and the pH-loading on shellfish-aquaculture areas.

Banned ports as of 2026

• Singapore: open-loop discharge banned within port waters since 1 January 2020. Hybrid scrubbers must operate in closed-loop mode within Singapore port limits. The ban is enforced by the Maritime and Port Authority of Singapore (MPA) and applies to anchorages and the entire port of Singapore.
• China (multiple ports): open-loop discharge banned in inland waters and inland ports since 1 January 2019. The ban was extended to coastal Domestic Emission Control Areas (DECAs) in 2020 and to all PRC ports in 2022. The ban is enforced by the Maritime Safety Administration (MSA) and applies to the Yangtze and Pearl River systems and the principal coastal ports.
• United Arab Emirates (Fujairah, Khor Fakkan): open-loop discharge banned in port waters since 2020. Fujairah is one of the world’s three largest bunker hubs, so the ban reshapes the regional scrubber economics.
• Oman: open-loop discharge banned in port waters since 2020.
• United States (California): open-loop discharge prohibited within 24 nautical miles of the California coast under the California Air Resources Board (CARB) Ocean-Going Vessel Fuel Rule, since 2009 (predating the IMO 2020 cap).
• Belgium, Netherlands (port waters): open-loop discharge restricted in the Antwerp-Bruges and Rotterdam port areas, with hybrid mode required at berth.
• Norway (fjords): open-loop discharge banned in defined fjord-tourism waters under the Norwegian Maritime Authority regulations, with the West Norwegian Fjords World Heritage Sites (Geirangerfjord, Naeroyfjord) subject to a specific ban from 2026 in conjunction with zero-emission requirements.

Compliance implications

A scrubber-equipped ship trading to multiple ports must verify the open-loop status at each port of call before berthing. The principal industry resource is the Cleantech Maritime open-loop ban registry, maintained as a dynamic list and incorporated into class-society advisory bulletins. Hybrid-scrubber ships have full operational flexibility (open-loop at sea, closed-loop in port). Open-loop-only ships are restricted to ports without bans and must use compliant fuel (VLSFO or MGO) at banned ports, requiring a fuel-changeover at the port-state boundary similar to the SECA changeover.

Future trajectory

The list of ports banning open-loop discharge has expanded steadily from 2019 to 2026. The trajectory suggests that by 2030 most major port states will impose either a complete ban or a closed-loop-mode requirement at berth. The 2024 EU Maritime Working Group recommendation for an EU-wide port-water open-loop ban has not yet been adopted but is under active discussion.

Alternative compliance: LNG, methanol, ammonia, biofuels

The third compliance pathway under Reg 14 is alternative low-sulphur fuels that are intrinsically below 0.10% by virtue of their chemistry.

LNG (Liquefied Natural Gas)

LNG is essentially sulphur-free (typical sulphur content <10 ppm or <0.001%, i.e. orders of magnitude below SECA cap). LNG combustion produces zero SOx and substantially reduced PM versus residual fuel oil. LNG is therefore inherently compliant with both Reg 14 global cap and SECA cap without scrubber or fuel-quality concerns.

The LNG pathway has grown substantially in the 2020 to 2026 window: approximately 1,200 LNG-fuelled ships in service or on order by 2026, predominantly LNG carriers (using boil-off gas), large container ships, RoRo ferries and PCTC car carriers. The capital cost premium for LNG dual-fuel propulsion is approximately USD 15 to 25 million per ship, partially offset by the lower operating cost of LNG fuel versus VLSFO/MGO and by the absence of scrubber operating costs.

The LNG pathway has a separate concern under the Net-Zero Framework: methane slip from LNG dual-fuel engines (particularly the Otto-cycle low-pressure engines like the Wartsila DF and the MAN ME-GA) gives LNG a less favourable life-cycle GHG profile than headline CO2-only comparisons would suggest (see the per-fuel WTW LNG Otto/diesel page). The Reg 14 sulphur compliance is unaffected by methane slip; the slip is a Net-Zero (Reg 28) concern.

Methanol

Methanol (CH3OH) is sulphur-free by chemical structure. Methanol combustion produces zero SOx and substantially reduced PM. Methanol has emerged as a serious alternative fuel from approximately 2020 onwards, with major orders for methanol dual-fuel container ships (Maersk, CMA CGM, COSCO, ONE, Hapag-Lloyd) reaching approximately 300 ships on order by 2026. The methanol pathway has been favoured by container-ship operators because methanol is liquid at ambient conditions (no cryogenic storage), the bunkering infrastructure draws on existing chemical-tanker logistics, and renewable methanol (e-methanol or bio-methanol) offers a Net-Zero compliance pathway not available for LNG.

Ammonia

Ammonia (NH3) is sulphur-free and carbon-free by chemical structure. Ammonia combustion produces zero SOx and zero CO2. The ammonia pathway is at an earlier deployment stage (approximately 30 ammonia-fuelled ships on order by 2026, principally bulk carriers), with the first deliveries expected in 2026 to 2027. Ammonia has separate operational concerns (toxicity, NOx emissions from ammonia combustion requiring SCR for Tier III compliance, ammonia slip) but is fully compliant with Reg 14.

Biofuels

Biofuels (HVO, FAME, sustainable bunker fuel oil) typically have <0.10% sulphur content, depending on feedstock. Biofuels have emerged from approximately 2022 as a drop-in compliance pathway for both Reg 14 and Net-Zero, with FAME blends and pure HVO offered at major bunker ports (Rotterdam, Singapore, Algeciras). The biofuel pathway is constrained by feedstock availability and cost (typically USD 200 to 400/t premium over VLSFO) and is most economically deployed in conjunction with Net-Zero (Reg 28) compliance rather than for Reg 14 compliance alone.

Hydrogen

Hydrogen (H2) is sulphur-free and carbon-free. Hydrogen-fuelled ships are at the demonstration stage in 2026 (a handful of small inland and coastal vessels, mostly ferries) and have not yet reached commercial deep-sea deployment. Hydrogen storage at sea is the principal technical constraint (cryogenic at −253°C or compressed at 350 bar+), and the pathway is unlikely to reach significant scale before 2030.

In-service compliance: BDN, sample, PSC XRF testing

In-service compliance verification under Reg 14 is built on three layers: documentary evidence in the Bunker Delivery Note, physical evidence in the MARPOL one-litre fuel sample, and external evidence from port-state-control sampling and analysis.

Bunker Delivery Note (Reg 18 cross-link)

The BDN is the documentary basis for sulphur compliance. Under Regulation 18, every bunker transaction is accompanied by a BDN listing the fuel sulphur content (declared by the bunker supplier and presumed accurate). The ship retains the BDN for three years after the bunker transaction and produces it on demand to PSC.

A BDN showing sulphur ≤0.50% is presumptive evidence of global-cap compliance. A BDN showing sulphur ≤0.10% is presumptive evidence of SECA compliance. PSC inspection examines the BDN at first call and confirms it matches the ship’s fuel consumption pattern (cross-checking against the Oil Record Book and the engine data).

MARPOL one-litre fuel sample

Each bunker transaction produces a MARPOL one-litre fuel sample, taken at the bunker manifold during the transfer, sealed and signed by both the bunker supplier and the ship’s chief engineer. The sample is retained on board for twelve months (or until the fuel is consumed and the next bunker is taken, whichever is later) under Reg 18.6.

The MARPOL sample is the definitive evidence of the fuel sulphur content at the time of bunkering. PSC inspection may direct the sample to an accredited laboratory for ISO 8754 sulphur analysis, with the result determining compliance independent of the BDN declaration. A BDN-sample mismatch (BDN claims 0.40% but the sample analyses at 0.55%) is treated as a sulphur-cap breach plus a Reg 18 BDN-accuracy violation.

PSC portable XRF testing

Modern PSC inspection commonly uses portable X-ray fluorescence (XRF) analysers at the dock to test fuel samples in real time, without sending to laboratory. Portable XRF gives a sulphur-content reading within approximately ±5% of the laboratory ISO 8754 value at the 0.10 to 1.0% range, sufficient for screening compliance. The XRF reading is treated as screening evidence that can be confirmed by laboratory analysis if challenged.

PSC inspection commonly tests:

• Service-tank fuel sample (the fuel currently being burnt by the engines).
• Storage-tank fuel sample (the fuel currently being held for future use).
• MARPOL one-litre sample (the bunkered fuel sample).

A discrepancy between any two readings is investigated. The most common discrepancy is between the BDN-declared value and the service-tank sample: if BDN claims 0.40% and the service-tank XRF reads 0.55%, the explanation is typically either BDN-supplier mis-declaration, in-ship fuel mixing, or post-bunker contamination. The investigation determines liability.

Scanning electron microscope (SEM) for residue analysis

For detailed compliance investigations (typically in cases of suspected scrubber bypass or fuel-mixing fraud), PSC may use scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) on the exhaust-soot residue or on the fuel-tank residue. The SEM analysis provides elemental composition (sulphur, vanadium, nickel, sodium, calcium) and can fingerprint the fuel against a known crude-oil source.

Fuel oil verification procedure: Appendix VI and the 0.59R rule

Annex VI Appendix VI (introduced by the 2021 amendments, entering force 1 April 2022) codifies the verification procedure for fuel oil samples taken during PSC inspection. The procedure distinguishes three sample types by their regulatory function:

• The MARPOL delivered sample (the Reg 18.6 one-litre sample taken at the bunker manifold during delivery): the primary evidentiary record of what was supplied. The sample is sealed by both the bunker supplier and the ship’s representative and retained on board for 12 months. If laboratory analysis confirms sulphur above the cap, liability falls initially on the supplier.
• The in-use fuel oil sample (taken from the service tank or from the fuel supply line immediately before the engine): evidence of what the ship is actually burning at the time of inspection. The in-use sample is the primary PSC enforcement tool.
• The onboard fuel oil sample (taken from storage tanks): evidence of what the ship is holding for future use, relevant to the carriage ban under MEPC.305(73).

For in-use and onboard samples, Appendix VI applies a statistical tolerance to account for measurement reproducibility. The guideline limit for the in-use sample is not the nominal cap but the cap plus 0.59R, where R is the reproducibility of the ISO 8754 test method at the relevant sulphur level. At the 0.50% cap, R is approximately 0.05% m/m, so the in-use sample must read at or below approximately 0.53% m/m before a PSC officer treats the result as a confirmed breach. A reading between 0.50% and 0.53% triggers re-testing rather than immediate action.

For the MARPOL delivered sample, no tolerance is applied: the delivered sample represents what was contractually supplied, and the declared BDN value is compared to the ISO 8754 result without a reproducibility correction. A BDN declaring 0.48% against a laboratory result of 0.52% is therefore a Reg 18 accuracy finding against the supplier.

The Fuel Oil Non-Availability Report (FONAR) procedure allows a ship to use non-compliant fuel when a genuine good-faith effort to bunker compliant fuel fails. FONAR is not a self-certified exemption: it must be filed in advance with the flag administration and notified to the port state. The IMO 2019 Guidelines on consistent implementation (Resolution MEPC.320(74)) include a standard FONAR template. A FONAR does not exempt the ship from port-state investigation; it creates a rebuttable presumption of good faith that PSC may accept or reject based on the bunkering record. Repeat FONAR filings by the same ship on the same route draw heightened scrutiny.

Compliance rate trajectory

The non-compliance rate measured through PSC inspection has trended downward since 2015:

• 2015 (first year of 0.10% SECA): about 5 to 8% in the North Sea SECA, declining through 2016 to 2019.
• 2020 (first year of 0.50% global cap): about 5% globally, with regional variation.
• 2024: about 1% globally.

The Tokyo MoU and Paris MoU concentrated inspection campaigns on the 2020 sulphur cap (described in the next section) drove the downward trajectory.

Tokyo MoU + Paris MoU IMO 2020 campaign 2020-2022

The Tokyo MoU (Asia-Pacific) and Paris MoU (Europe + North Atlantic Canada) regional port-state-control regimes conducted Concentrated Inspection Campaigns (CICs) on the IMO 2020 sulphur cap in the 2020 to 2022 window.

Paris MoU CIC 2020

The Paris MoU CIC on Annex VI ran from 1 September to 30 November 2020, three months of intensified PSC inspection across the 27 Paris MoU member states. The CIC inspected approximately 3,200 ships at Paris MoU ports, with the principal findings:

• 96% of inspected ships had a valid IAPP Certificate.
• 94% of inspected ships had a Bunker Delivery Note for the most recent bunker.
• 5.2% of inspected ships had a sulphur non-compliance finding at first inspection.
• 2.1% had a non-compliance confirmed by laboratory analysis after MARPOL-sample testing.
• 18 detentions were issued for serious non-compliance, principally for ships found burning HSFO without a scrubber after 1 March 2020.

Tokyo MoU CIC 2020

The Tokyo MoU CIC on Annex VI ran from 1 September to 30 November 2020 in parallel with the Paris MoU campaign, across the 21 Tokyo MoU member states. The CIC inspected approximately 5,500 ships at Tokyo MoU ports, with the principal findings:

• 97% valid IAPP Certificate.
• 95% valid BDN.
• 6.4% sulphur non-compliance at first inspection.
• 2.7% confirmed by laboratory analysis.
• 23 detentions issued.

Combined campaign findings

The combined Paris + Tokyo MoU 2020 CIC findings showed the global non-compliance rate at approximately 5% in the first year of the 0.50% cap, declining to approximately 2% by 2022 and approximately 1% by 2024. The CIC methodology became the model for subsequent CICs, including the 2025 Mediterranean SECA CIC (preliminary results indicated a 4 to 6% non-compliance rate in the first six months, declining as the market settled).

Detention statistics

Detentions are issued for serious non-compliance, typically:

• Operating without a valid IAPP Certificate.
• Carrying HSFO above 0.50% without a scrubber and without a documented compliant-fuel-not-available notification.
• Bypassing or disabling a scrubber on a scrubber-equipped ship while burning HSFO.
• Gross BDN-sample mismatch indicating supplier or operator fraud.

A detention extends the port stay until the non-compliance is rectified (typically a few days to two weeks), with associated commercial losses of USD 50,000 to 500,000 per day depending on ship type. The detention is recorded in THETIS-EU and Tokyo MoU databases and increases the inspection priority for subsequent calls (including the next call at any MoU port worldwide).

2024 PM black carbon Arctic regulation debate

A separate debate at the IMO Marine Environment Protection Committee from 2023 onwards concerns black carbon emissions in the Arctic and whether to adopt a separate regulation under Reg 14 or a new Reg 14A.

Black carbon basics

Black carbon (BC) is a component of particulate matter, formed from incomplete combustion of fuel hydrocarbons. BC has an exceptionally strong albedo-warming effect when deposited on Arctic snow and ice: each tonne of BC deposited on Arctic snow has a warming effect equivalent to approximately 1,500 tonnes of CO2 over a 20-year horizon. Ship-source BC, while small in mass terms (approximately 60 to 100 thousand tonnes per year globally) compared with CO2 (approximately 950 million tonnes per year from shipping), has a disproportionate climate impact in the Arctic.

Reg 14 partial coverage

Reg 14 reduces BC indirectly by reducing the secondary sulphate aerosol that nucleates BC particles, but does not directly limit BC emission. The 0.10% sulphur cap reduces BC by approximately 10 to 20% compared with HSFO baseline, principally because lower-sulphur distillate fuels have lower aromatic content and produce less coke. The 0.50% global cap reduces BC less (approximately 5 to 10% reduction).

Arctic-specific proposals

The 2023 to 2026 debate at MEPC has explored several proposals:

• Distillate-only fuel mandate in Arctic: a requirement that all Arctic-transit ships use distillate fuel (DMA grade or equivalent) only, prohibiting residual fuels even at 0.10% sulphur. The proposal is supported by the Arctic Council coastal states (Canada, Denmark/Greenland, Norway, Russia, USA/Alaska) but has not yet reached MEPC consensus.
• Aromatic-content limit: a numerical cap on aromatic content of marine fuel in Arctic, indirectly reducing BC. Technically straightforward but politically contested.
• BC mass emission limit: a direct numerical cap on BC mass emission per kWh, requiring on-board BC monitoring. The proposal has the most environmental certainty but the greatest implementation cost.
• Arctic SECA + black-carbon combined: combining the proposed Canadian Arctic SECA with a black-carbon distillate mandate as a joint instrument.

The current trajectory, as of MEPC 84 in October 2026, suggests the Canadian Arctic SECA + distillate mandate combined approach is most likely to be adopted, with effective date potentially 1 January 2030. This would be the first marine regulation directly addressing BC, separate from but parallel to the Reg 14 sulphur framework.

Industry response

The shipping industry through the International Chamber of Shipping (ICS) and BIMCO has supported the principle of Arctic BC reduction but has cautioned against highly prescriptive distillate-only requirements that could constrain the very low fleet of dedicated Arctic-trade vessels. The industry preference is for a flexibility provision allowing scrubber compliance with BC removal certification, similar to the Reg 14 scrubber pathway.

Reg 14.7 fuel oil quality requirements

In addition to the sulphur cap, Reg 14 includes paragraph 14.7 establishing fuel oil quality requirements that apply to any fuel oil delivered to a ship. The Reg 14.7 quality requirements are a subset of the broader Regulation 18 framework but are integral to the Reg 14 sulphur regime.

Fuel oil quality requirements

Reg 14.7 requires that fuel oil delivered to ships:

• Be derived by distillation, processing or refining of crude oil, or alternatively be a product of the transesterification or hydroprocessing of vegetable, animal or aquatic biomass (i.e. legitimate biofuels are accepted).
• Not include inorganic acid in any concentration.
• Not include chemical waste or other waste materials beyond normal refinery streams.
• Not jeopardise the safety of the ship or adversely affect the performance of the machinery.
• Not be harmful to personnel in normal handling.
• Not contribute to additional air pollution beyond what is implied by the sulphur cap.

ISO 8217 implementation

The Reg 14.7 quality requirements are operationally implemented through ISO 8217 fuel-oil specifications. ISO 8217:2017 (the current edition) defines the bunker-grade specifications for residual marine fuels (RMA, RMB, RMD, RME, RMG, RMK), distillate marine fuels (DMA, DMZ, DMB, DMX) and dual-fuel grades. ISO 8217:2024 (in preparation) will introduce dedicated grades for VLSFO, ULSFO and biofuels.

ISO 8217 specifies numerical limits for sulphur, viscosity, density, flash point, pour point, water content, ash content, vanadium, sodium, aluminium + silicon (cat-fines), CCAI (calculated carbon aromaticity index), total sediment potential and microbial contamination. Compliance with ISO 8217 is presumptive evidence of compliance with Reg 14.7.

Cat-fines limit

The most operationally important quality parameter is the aluminium + silicon (cat-fines) limit, set at 60 mg/kg in ISO 8217:2017 for residual fuels (60 ppm). Cat-fines are catalyst residues from refinery FCC operations that, if not removed by purifier on the ship, cause severe wear of fuel pumps, injectors, piston rings and cylinder liners. The cat-fines limit is a recurring source of dispute in the bunker market, with bunker-supply incidents involving cat-fines >60 ppm leading to BDN claims and engine damage claims.

Stability and compatibility

VLSFO (post-2020) has introduced new stability and compatibility concerns: VLSFO blends from different sources can be incompatible (mixing produces asphaltene precipitation and sediment), and VLSFO blends can be unstable in storage (asphaltene precipitation over 30 to 60 days even without mixing). ISO 8217:2017 includes a total sediment potential test (ISO 10307-2) for stability. Industry practice now mandates compatibility tests before bunker-mixing, typically using the ASTM D7060 spot-test or laboratory turbidity method.

Class society implementation: DNV, LR, ABS, BV, NK, RINA, KR, CCS, RS, IRS

The Reg 14 implementation framework relies on the IACS class societies for type-approval surveys, ship-installation surveys, periodic compliance surveys and EGCS certificate issuance under flag-state delegation.

Class type-approval programmes

The principal class type-approval programmes for scrubber units are:

• DNV (Det Norske Veritas): the largest class by scrubber type-approval market share, approximately 35% of the global installed scrubber base. DNV operates type-approval centres in Hovik (Norway), Hamburg, Singapore and Shanghai.
• Lloyd’s Register (LR): approximately 20% of the global installed scrubber base. LR operates type-approval centres in London, Hamburg, Singapore, Shanghai and Busan.
• ABS (American Bureau of Shipping): approximately 15% of the global installed scrubber base. ABS operates type-approval centres in Houston, Singapore and Busan.
• Bureau Veritas (BV): approximately 10% of the global installed scrubber base. BV operates centres in Paris, Hamburg, Singapore and Shanghai.
• NK (ClassNK): approximately 8% of the global installed scrubber base, predominantly Japanese-flag and Japanese-owned ships. ClassNK operates centres in Tokyo, Singapore and Busan.
• RINA (Registro Italiano Navale): approximately 4% of the global installed scrubber base, predominantly Italian-flag ships and the Mediterranean fleet.
• KR (Korean Register): approximately 3% of the global installed scrubber base, predominantly Korean-flag and Korean-owned ships.
• CCS (China Classification Society): approximately 3% of the global installed scrubber base, dominant in Chinese-flag ships.
• RS (Russian Maritime Register): <2% of the global installed scrubber base, principally Russian-flag ships.
• IRS (Indian Register of Shipping): <1% of the global installed scrubber base, principally Indian-flag and South Asian fleet.

Class survey scope

Class survey scope under Reg 14 EGCS includes:

• Type-approval testing of the scrubber unit on a manufacturer test bed, demonstrating SO2 removal efficiency, wash-water criteria compliance, structural integrity and instrumentation accuracy.
• Installation survey on the ship, verifying the scrubber is installed per the type-approval drawings and the supporting instrumentation is functional.
• Commissioning survey at sea, verifying the scrubber operates within the type-approval envelope under realistic operating conditions.
• Annual surveys thereafter, verifying the scrubber continues to operate within the type-approval envelope and the wash-water and emission monitoring instruments are calibrated.
• Renewal surveys at five-year intervals, including detailed inspection of the scrubber tower internals, the wash-water treatment system, the seawater pumps and the funnel modifications.

IACS Recommendation 100

IACS Recommendation 100 of 2018 provides the common technical framework for EGCS type-approval, installation, commissioning and survey. Recommendation 100 has been incorporated into the individual class rules of all IACS members and is the principal harmonisation instrument across class societies. Recommendation 100 is updated biennially, with the most recent revision in 2024 incorporating MEPC.340(77) revised Guidelines.

Mutual recognition

A scrubber type-approved by one IACS class is mutually recognised by all other IACS classes for installation on ships of any IACS-class flag, subject to a flag-state-acceptance check. This mutual recognition reduces the multiple-class type-approval burden for scrubber manufacturers and is a key efficiency feature of the IACS framework.

VLSFO premium ~USD 100-200/t over HFO since 2020

The price premium of VLSFO over HSFO is the principal commercial parameter governing the scrubber-investment decision and the broader fuel-strategy decision under Reg 14.

2020 premium spike

In the first quarter of 2020 (immediately after the IMO 2020 cap entry into force), the VLSFO-HFO spread spiked to USD 250 to 350/t at major bunker hubs (Singapore, Rotterdam, Fujairah). The spike reflected:

• Refinery transition friction (some refineries ramping VLSFO production slowly).
• Logistics constraints (bunker barges and storage tanks having to dedicate to one or the other product, reducing flexibility).
• Demand-side dynamics (most non-scrubber ships requiring VLSFO immediately at the cap entry into force).

2021 to 2024 settlement

By Q2 2021 the spread had settled to USD 100 to 150/t, reflecting normal refinery operation and balanced supply-demand. The spread has remained in the USD 100 to 200/t range through 2022, 2023 and 2024, with seasonal variation (typically tighter spreads in summer when North American refineries optimise for residual production, wider spreads in winter when distillate demand competes with VLSFO blending). The all-time average from Q2 2021 through 2024 is approximately USD 130/t.

MGO premium

The MGO-HFO spread has been substantially wider than the VLSFO-HFO spread, typically USD 200 to 400/t, reflecting both the desulphurisation cost (deeper than VLSFO) and the distillate-supply cost (competing with road-diesel). The MGO premium has trended downward as distillate refineries optimise their slate, but remains structurally above the VLSFO premium.

Scrubber economics impact

The VLSFO-HFO spread is the principal driver of scrubber investment economics. The simple-payback formula (above) shows that:

• At USD 200/t spread: payback approximately 1 to 1.5 years.
• At USD 150/t spread: payback approximately 1.5 to 2.5 years.
• At USD 100/t spread: payback approximately 2.5 to 4 years.
• At USD 50/t spread: scrubber investment loses commercial sense; payback >5 years.

The 2024-2026 spread of approximately USD 100 to 150/t makes scrubber retrofit economics moderately attractive for new orders but marginal for retrofits to existing ships (where remaining ship life and dry-dock-cycle alignment matter). New scrubber retrofit orders peaked in 2019 (pre-cap, in anticipation of wide spreads), declined sharply in 2020 to 2022 (uncertainty about long-term spread), and have stabilised at approximately 200 to 400 retrofits per year from 2023 onwards.

Forward outlook

The forward outlook for the VLSFO-HFO spread depends on:

• The trajectory of refinery hydrocracker investments (more capacity tends to compress the spread).
• The trajectory of HFO demand (declining as scrubber fleet stabilises tends to widen the spread, since marginal HFO buyer is squeezed).
• Net-Zero compliance pathways (LNG, methanol, ammonia displacing both VLSFO and HFO tends to compress both, with relative effect uncertain).

The consensus industry view as of 2026 is that the spread will remain in the USD 100 to 200/t range through 2030, with gradual narrowing as scrubber-fleet stabilisation reduces HFO demand and refinery investments increase VLSFO supply.

Scrubber payback economics ~1-3 years

The scrubber payback period is the principal commercial decision metric for scrubber investment. The simple-payback formula is:

with typical values:

• C_capex = USD 4 to 8 million for a typical post-Panamax container ship or VLCC tanker.
• (P_VLSFO − P_HSFO) = USD 100 to 200/t (the VLSFO-HSFO spread).
• m_fuel,annual = 15,000 to 30,000 t/year for the same ship class.
• C_opex = USD 200,000 to 400,000/year (caustic for closed-loop, maintenance, monitoring).

Worked examples

VLCC tanker (annual fuel 30,000 t, USD 5M scrubber, USD 150/t spread, USD 250k/year opex):

Post-Panamax container ship (annual fuel 25,000 t, USD 6M scrubber, USD 150/t spread, USD 300k/year opex):

Capesize bulker (annual fuel 18,000 t, USD 5M scrubber, USD 150/t spread, USD 250k/year opex):

Handysize bulker (annual fuel 6,000 t, USD 4M scrubber, USD 150/t spread, USD 200k/year opex):

The handysize case shows that scrubber economics do not work for small ships with low annual fuel consumption: the fixed capex amortises over too few tonnes of fuel for the spread to recover the investment in a reasonable period. Scrubbers have therefore concentrated in the large-ship segment (VLCC tankers, capesize bulkers, post-Panamax container ships), with virtually no penetration in handysize, MR tanker or small container-ship segments.

Discounted payback and NPV

A more rigorous analysis uses discounted payback with a typical discount rate of 8 to 10% per year and a remaining ship-life of 10 to 20 years. Discounted-payback periods are typically 0.2 to 0.5 years longer than simple payback, but the conclusion is similar: scrubber investment is attractive at USD 150/t spread and above for large ships, marginal for medium ships, and unattractive for small ships.

Risk premium for spread volatility

The VLSFO-HFO spread is not constant: it has varied between USD 50/t and USD 350/t in the 2020 to 2026 window. A risk-adjusted scrubber business case must include a spread-volatility scenario, typically modelled as a normal distribution around the historical mean. At one standard deviation below the mean (approximately USD 80/t), the payback periods extend by approximately 50%, which can shift the decision for marginal cases.

Future scrubber investment

The forward scrubber-investment market is approximately 200 to 400 retrofits per year from 2023 onwards, predominantly in the large-tanker, capesize-bulker and post-Panamax-container segments. The trend has stabilised after the 2019 peak (approximately 1,800 retrofit orders in 2019 alone), and the industry has settled into a steady-state replacement and incremental-build pattern. Approximately 25 to 30% of the global tanker and bulker fleet is scrubber-equipped as of 2026, with limited further penetration expected.

SECA-shifting effect on routeing

A subtle but quantifiable consequence of Reg 14 is the SECA-shifting effect on routeing, where ships re-route to minimise the time spent in SECAs to reduce fuel cost.

Mechanism

A non-scrubber ship trading from Asia to Northern Europe must transit the European SECA boundary at some point on the voyage. The SECA boundary defines the cutover from VLSFO at the global cap (0.50%) to MGO at the SECA cap (0.10%). The cost difference is approximately USD 200 to 400/t (the MGO-VLSFO spread). For a ship burning 100 t/day, an extra day in SECA costs USD 20,000 to 40,000.

The ship operator therefore has an economic incentive to minimise SECA transit time, which translates into specific routeing choices:

• Shortest path through SECA: enter the SECA at the closest boundary point to the destination, exit at the closest boundary point on the return.
• Avoid SECA where alternative routes exist: a ship trading from Singapore to St Petersburg can route via Suez and the Mediterranean (no SECA in 2024) or via the Cape and the Atlantic (no SECA outside the North Sea SECA). The Suez route is faster but enters the Mediterranean SECA from 1 May 2025; the Cape route is slower but minimises SECA transit.
• Bunker port choice: bunker the SECA-grade MGO at a port near but outside the SECA, minimising the SECA transit before the changeover. For European trades, Algeciras, Las Palmas and Gibraltar are common pre-SECA bunker ports.

Quantitative effect

The SECA-shifting effect on routeing has been quantified by several academic and industry studies:

• 2017 ICCT study: SECA designation increased Mediterranean transit traffic by approximately 5 to 10% as ships preferred Mediterranean route to North Sea, until Mediterranean was designated.
• 2020 Lloyd’s List study (post-IMO 2020): SECA-equivalent routeing effect on global trades modest at the 0.50% global cap level, since global cap nearly eliminated the spread effect outside SECA.
• 2025 industry analysis (post-Mediterranean SECA): residual routeing effect is small as nearly all major routes are now SECA-affected.

Implications

The SECA-shifting effect was substantial in the 2015 to 2020 window when the SECA cap (0.10%) was much tighter than the global cap (3.50%), creating a large fuel-cost incentive to avoid SECA. The shift has narrowed since 2020 with the global cap at 0.50%, since the SECA-vs-global differential is now only 0.40 percentage points rather than 3.40 percentage points. The Mediterranean SECA designation in 2025 has further narrowed the effect by extending SECA coverage. The SECA-shifting effect is now operationally minor and is unlikely to drive significant routeing change in the 2025 to 2030 window.

IMO Net-Zero Framework intersection (intensity not SOx)

The IMO Net-Zero Framework governs life-cycle GHG-intensity of marine fuels (CO2-equivalent per megajoule energy) and is a separate regulatory regime from Reg 14 sulphur. MEPC 83 in April 2025 approved the framework as a draft new Chapter 5 of Annex VI; MEPC/ES.2 in October 2025 was convened to formally adopt it but adjourned without adoption. Negotiations resume in 2026. The intersection between the two regimes is primarily through the alternative-fuel pathway.

Net-Zero scope

The Net-Zero Framework as approved at MEPC 83 targets a 1 January 2027 entry into force (conditional on formal adoption) and requires:

• Annual reduction of fleet-average GHG intensity from a 2019 baseline of approximately 91.6 g CO2e/MJ.
• Reduction trajectory: 5% by 2027, 17% by 2030, 27% by 2035, 65% by 2040, 100% (net zero) by 2050.
• Trading mechanism: surplus units issued for fuels below a target intensity, deficit penalties for fuels above.
• Penalty structure: contributions to the IMO Net-Zero Fund for fuels above the targeted intensity.

Reg 14 and Net-Zero intersection

The Reg 14 sulphur cap and the Net-Zero GHG-intensity targets interact through the alternative-fuel pathway:

• LNG: sulphur ≤0.001%, fully Reg 14 compliant. GHG intensity (well-to-wake) approximately 76 to 90 g CO2e/MJ (depending on methane slip), roughly equivalent to VLSFO. LNG is Reg 14 compliant but only marginally better on Net-Zero.
• Methanol (e-methanol): sulphur 0%, fully Reg 14 compliant. GHG intensity approximately 0 to 30 g CO2e/MJ (dependent on production pathway). Methanol is both Reg 14 compliant and Net-Zero compliant.
• Ammonia (green): sulphur 0%, fully Reg 14 compliant. GHG intensity approximately 0 to 20 g CO2e/MJ. Ammonia is both Reg 14 compliant and Net-Zero compliant.
• Biofuel (bio-MGO, FAME): sulphur ≤0.10%, fully Reg 14 compliant. GHG intensity approximately 5 to 30 g CO2e/MJ. Biofuel is both Reg 14 compliant and Net-Zero compliant.

No further SOx target

The Net-Zero Framework does not include any further SOx target beyond the existing 0.50% global cap and 0.10% SECA cap of Reg 14. The Net-Zero focus is on GHG (CO2, methane, N2O) and not on air-quality pollutants (SOx, NOx, PM). Reg 14 is therefore expected to remain at its current numerical levels indefinitely, with future tightening to occur via SECA expansion.

Practical implication

A ship operator planning a Net-Zero compliance strategy through alternative fuels (LNG, methanol, ammonia, biofuel) automatically satisfies Reg 14 as a side-effect of the Net-Zero choice. The principal exception is LNG with high methane slip, which satisfies Reg 14 but underperforms on Net-Zero compared with the headline expectations. Operators choosing LNG primarily for Reg 14 compliance (rather than Net-Zero) benefit from the simplicity but accept a less favourable Net-Zero trajectory.

Relationship to Reg 13 NOx (cross-link)

The Reg 14 SOx and PM regulation and the Reg 13 NOx regulation are independent regulatory regimes governing different pollutants, but they interact at multiple levels in practice.

Independent regulatory structure

• Reg 14 (SOx, PM): fuel-quality regime, applies to any combustion device on the ship, governed by the sulphur cap and the carriage ban.
• Reg 13 (NOx): engine-certification regime, applies to marine diesel engines >130 kW, governed by the Tier I/II/III limits and the NTC 2008.

The two regimes are administratively distinct (Reg 14 has the IAPP Certificate fuel-quality supplement; Reg 13 has the EIAPP Certificate per engine), but they share the IAPP Certificate as the ship-level umbrella document.

Joint ECA designations

Most ECAs are designated for both sulphur and NOx control:

• Baltic Sea: SECA from 2006 (sulphur), NECA from 2021 (NOx); joint ECA.
• North Sea: SECA from 2007 (sulphur), NECA from 2021 (NOx); joint ECA.
• North American: joint SECA + NECA from 2012 / 2016.
• US Caribbean: joint SECA + NECA from 2014 / 2016.

The Mediterranean, by contrast, is currently a sulphur-only ECA, with NECA designation under negotiation.

Compliance pathway interaction

The two regimes interact through the alternative-fuel pathway:

• LNG: compliant on both Reg 14 (sulphur ≈0%) and Reg 13 Tier III (Otto-cycle low NOx).
• Methanol: compliant on Reg 14 (sulphur 0%); Tier III compliance requires SCR or pilot-fuel optimisation depending on engine architecture.
• Ammonia: compliant on Reg 14 (sulphur 0%); Tier III compliance requires SCR for the ammonia-combustion NOx.
• Scrubber: Reg 14 compliance only (with HSFO). Does not address Reg 13 NOx.
• VLSFO/MGO: Reg 14 compliance only. Does not address Reg 13 NOx (the engine remains certified at Tier II globally; Tier III requires SCR or EGR).

EGR cross-effect

The EGR (exhaust gas recirculation) Tier III compliance pathway has a water scrubber loop that incidentally captures a fraction of SOx and PM from the recirculated exhaust. The EGR scrubber loop is not certified as a Reg 14 scrubber (the EGR loop is downstream of the engine charge-air system, not in the main exhaust path), but the SOx and PM reduction is a co-benefit. Ships using EGR for Tier III NOx therefore have a partial Reg 14 SOx reduction even when burning higher-sulphur fuel; this is operationally interesting but commercially minor since SECA fuel-grade requirements still apply.

Relationship to Reg 18 BDN (cross-link)

Regulation 18 of Annex VI governs fuel oil quality and the bunker delivery note (BDN). Reg 18 is the operational mechanism by which Reg 14 sulphur compliance is documented, sampled and verified.

BDN as Reg 14 documentary evidence

The BDN records every bunker transaction with the fuel sulphur content declared by the supplier. The BDN is the first line of evidence for Reg 14 compliance: a BDN showing sulphur ≤0.50% (global cap) or ≤0.10% (SECA cap) is presumptive evidence of compliance with Reg 14.

PSC inspection examines the BDN at first inspection. A BDN missing, unsigned by the supplier, or showing sulphur above the applicable cap is a Reg 14 finding plus a Reg 18 finding.

MARPOL one-litre sample

Each bunker transaction produces a MARPOL one-litre fuel sample (Reg 18.6) retained on board for twelve months. The sample is the definitive evidence of fuel sulphur at the time of bunker, used to verify the BDN declaration.

A BDN-sample mismatch is treated as a serious finding: the supplier may have mis-declared (a Reg 18 violation by the supplier, with potential commercial recourse from the ship), or the ship may have falsified the BDN (a Reg 18 violation by the ship), or the ship may have mixed fuel post-bunker (a Reg 14 violation if the resulting fuel exceeds the applicable cap).

Cross-check logic

PSC inspection cross-checks:

• BDN sulphur versus service-tank sample (ship-level XRF or laboratory).
• BDN sulphur versus storage-tank sample (ship-level XRF or laboratory).
• BDN sulphur versus MARPOL sample (laboratory ISO 8754).

A consistent picture across all four (BDN within cap, all samples within cap) confirms compliance. Any inconsistency triggers further investigation, with the MARPOL sample being the definitive arbiter.

Reg 18 calculator cross-link

The Reg 18 BDN calculator implements the BDN structure, the sulphur-cross-check logic and the MARPOL sample retention timeline. The calculator complements this Reg 14 wiki article by providing the operational documentation flow.

The cap and its lineage

Regulation 14 is two piecewise step functions in time, one for the global cap and one for the SECA cap, plus the combustion stoichiometry that converts a fuel-sulphur fraction into an SO2 mass. The global cap reads:

and the SECA cap, offset earlier and five times tighter, reads:

Both step functions trace back to the 2008 amendments by Resolution MEPC.176(58). The 0.50% global step took effect 1 January 2020 after MEPC.280(70) of 2016 confirmed the date, and the 0.10% SECA step took effect 1 January 2015. The legacy steps were 4.50% (1997 to 2011), 3.50% (2012 to 2019), 1.50% (pre-July 2010) and 1.00% (July 2010 to 2014).

The sulphur in the fuel oxidises in the cylinder to SO2. Organosulphur compounds (mercaptans, thiophenes, sulphides, polysulphides) decompose above about 1,200°C and oxidise, in simplified form, as:

The SO2 yield runs 95 to 99% of the input sulphur, with the remaining 1 to 5% leaving as SO3 or as sulphate aerosol. For Reg 14 accounting the conversion is treated as complete, so the emission per tonne of fuel is:

Here $m_{\text{fuel}}$ is the fuel mass in tonnes, $c_{\text{S}}$ the sulphur fraction (0.005 for 0.50%), and the molecular-mass ratio $M_{\text{SO}_2}/M_{\text{S}} = 64/32 = 2.0$. So 1% sulphur in fuel produces about 20 kg SO2 per tonne of fuel burnt. For 1% S that is 10 kg of S per tonne of fuel, which forms 20 kg of SO2.

Scrubber equivalence

A scrubber-equipped ship that keeps burning high-sulphur fuel oil must prove its exhaust is no dirtier than compliant fuel would be. The MEPC.184(59) Guidelines and the MEPC.340(77) revision set the equivalence as an SO2/CO2 ratio ceiling:

where $R_{\text{cap}}$ is the ratio limit for the equivalent compliant-fuel sulphur content: 4.3 ppm at 0.10%, 21.7 ppm at 0.50%, 43.3 ppm at 1.00%, 65.0 ppm at 1.50%, and 195.0 ppm at 4.50%. A scrubber washing 3.50% S HSFO must therefore reach at least 86% removal for the 0.50% global-equivalent ratio, or 97% for the 0.10% SECA-equivalent ratio.

The open-loop wash-water discharge must also meet four numerical criteria at the discharge port:

The pH limit of 6.5 sits below the threshold where shellfish and coral larvae suffer calcium-carbonate dissolution; natural seawater is pH 8.0 to 8.2, so the 6.5 floor leaves margin for the plume to re-equilibrate within a metre or two of the hull. The PAH limit of 50 µg/L comes from the LC50 for marine zooplankton against typical PAH compounds with a safety factor near 100, normalised to 45 m³/MWh wash-water flow so the at-sea burden is independent of scrubber design.

The carriage ban under MEPC.305(73), effective 1 March 2020, is the enforcement spine: a non-scrubber ship that merely has non-compliant fuel oil on board is in breach regardless of whether it burned any. Only an approved EGCS lets a ship carry HSFO above 0.50% for use through the scrubber.

The scrubber business case is a simple payback on the VLSFO-to-HSFO price spread, which stabilised at about 100 to 200 USD/t after 2020:

The numerator is the capital cost; the denominator is the annual fuel-cost saving net of operating cost. It assumes a constant spread, constant annual fuel burn, and a constant operating cost, and it carries no time discount. A discounted analysis at an 8 to 10% rate extends the period by roughly 0.2 to 0.5 years.

Worked example

Take a VLCC tanker burning 30,000 t/year, trading Ras Tanura (Persian Gulf, no SECA) to Rotterdam (North Sea SECA) and back. The numbers below are illustrative inputs, not quoted prices.

Before 2020, under the 3.50% global cap and the 0.10% SECA cap from 2015:

• Outside SECA: 25,000 t HFO at 3.50% S gives SO2 = 25,000 × 2 × 0.035 = 1,750 t/year.
• Inside SECA: 5,000 t MGO at 0.10% S gives SO2 = 5,000 × 2 × 0.001 = 10 t/year.
• Total 1,760 t/year SO2. Fuel cost 25,000 × 380 (HFO) + 5,000 × 600 (MGO) = USD 12.5M/year.

After 2020, under the 0.50% global cap with no scrubber:

• Outside SECA: 25,000 t VLSFO at 0.50% S gives SO2 = 25,000 × 2 × 0.005 = 250 t/year.
• Inside SECA: 5,000 t MGO at 0.10% S gives 10 t/year.
• Total 260 t/year SO2, an 85% cut against pre-2020. Fuel cost 25,000 × 510 (VLSFO) + 5,000 × 700 (MGO) = USD 16.25M/year.

After 2020, with a scrubber and continued HSFO:

• Outside SECA: 25,000 t HSFO at 3.0% S, 98% scrubber removal, gives SO2 = 25,000 × 2 × 0.030 × 0.02 = 30 t/year.
• Inside SECA: 5,000 t MGO (most ports require closed-loop, and most operators prefer changeover) gives 10 t/year.
• Total 40 t/year SO2. Fuel cost 25,000 × 360 (HSFO) + 5,000 × 700 (MGO) = USD 12.5M/year, the same fuel cost as pre-2020.
• Add USD 5M scrubber capex once and USD 250k/year opex. The annual cash benefit against the no-scrubber post-2020 case is 16.25 − 12.5 − 0.25 = USD 3.5M/year, so payback is 5.0 / 3.5 ≈ 1.4 years.

The example shows the 85% mass cut from IMO 2020, the USD 3.75M/year penalty of fuel-grade switching, and the scrubber path returning the fuel bill to pre-2020 levels with a 1.4-year payback.

Regulatory basis

The instruments that build the Reg 14 regime are:

• MARPOL Annex VI Regulation 14: scope, sulphur-cap definitions, the SECA framework, and the Reg 14.7 fuel-quality requirements.
• Resolution MEPC.176(58): the 2008 amendments establishing the stepped-cap schedule.
• Resolution MEPC.280(70): the 2016 confirmation of 1 January 2020 as the 0.50%-cap date.
• Resolution MEPC.305(73): the 2018 carriage-ban amendments, effective 1 March 2020.
• Resolution MEPC.184(59) and Resolution MEPC.340(77): the 2009 EGCS Guidelines and the 2021 revision.
• Resolution MEPC.116(51), MEPC.117(52), MEPC.190(60), MEPC.202(62) and MEPC.361(79): the Baltic, North Sea, North American, US Caribbean and Mediterranean SECA designations.
• MEPC.1/Circ.899 and MEPC.1/Circ.900 (2022): the MEPC 78 guidance circulars on EGCS discharge water risk assessment and port reception of EGCS residues.
• ISO 8217:2017 and ISO 8754: bunker-fuel specifications and the laboratory sulphur-analysis method.

Common misreadings

Several errors recur in practice. The global cap (0.50% from 2020) and the SECA cap (0.10% from 2015) are distinct regimes applied by geography, not by date, and 0.50% was never the global cap before 2020 (it was 3.50% from 2012 and 4.50% before that). The carriage ban under MEPC.305(73) took effect 1 March 2020, two months after the cap itself on 1 January 2020; they are different instruments. VLSFO is defined by sulphur content (≤0.50%) only, so its physical properties vary widely and blend incompatibility is a real operational risk. Reg 14 sets the cap while Reg 18 sets the documentary mechanism that verifies it. A scrubber type-approval covers one engine-scrubber-fuel combination and is not a one-time pass; annual class surveys check continued compliance. A SECA (sulphur, Reg 14) is not the same as a NECA (NOx, Reg 13): most major ECAs are both, but the Mediterranean SECA in 2026 is sulphur-only. The 0.10% SECA grade is dominated by distillate MGO, not by a 0.10% residual ULSFO, which is technically possible but commercially minor. And the wash-water pH ≥6.5 limit applies at the discharge port, not to the inlet water (pH 8.0 to 8.2, no regulatory limit).

Limitations

This article carries practitioner caveats rather than completeness claims. The most important limitation is that the SO2/CO2 ratio method is only an equivalent: it certifies the exhaust against a compliant-fuel ratio, but it assumes a fuel carbon content in the normal 84 to 88% range. The MEPC.184(59) ratio of 13.0:1 grams SO2 per kilowatt-hour to percent sulphur, and the ppm ratio limits derived from it, drift if the actual carbon fraction departs from that band, for example with some biofuel or methanol-blend pilot fuels. Treat the ratio as a screening equivalence, not an exact mass balance.

Compliant fuel is not always available. Reg 14.6 and the IMO Fuel Oil Non-Availability Report (FONAR) procedure, standardised in the template at Resolution MEPC.320(74), let a ship use non-compliant fuel when a documented good-faith effort to source compliant fuel fails, with written notification to the flag and port states before the non-compliant fuel is used. FONAR is a narrow exception, not a routine pathway. Port states are explicitly not bound to accept a FONAR as a complete defence; they may investigate the bunkering record and the voyage history. Operators who file FONAR repeatedly on the same route draw heightened scrutiny and may face formal investigation under their flag administration.

Open-loop scrubber compliance under the IMO Guidelines does not guarantee local lawfulness. A growing list of port states, including Singapore, China, the UAE (Fujairah, Khor Fakkan), Oman and California, bans open-loop discharge in their waters even where the discharge meets the MEPC.184(59) criteria. An open-loop-only ship trading to those ports must switch to closed-loop, where fitted, or burn VLSFO or MGO, which is a real limitation on the scrubber pathway that the SO2/CO2 ratio alone does not capture.

Fuel compatibility and stability are open risks under the 0.50% cap. VLSFO blends from different sources can be incompatible (mixing precipitates asphaltenes and damages fuel pumps and injectors) and can be unstable in storage over 30 to 60 days even without mixing. ISO 8217:2017 added the ISO 10307-2 total-sediment-potential test, but the test predicts rather than prevents the problem, so bunker-vetting and compatibility spot-tests before mixing remain the operator’s responsibility.

The worked example and the payback figures are estimates, not quoted prices. The USD figures for HFO, VLSFO and MGO, the spread, the scrubber capex and the opex are illustrative inputs chosen to show the method. The simple-payback formula ignores the time value of money, treats the spread and the annual fuel burn as constant, and omits off-hire and dry-dock scheduling effects. The spread alone has ranged from about USD 50/t to USD 350/t since 2020, and at one standard deviation below the mean the payback periods extend by roughly half, which can flip a marginal retrofit decision. Run the numbers against your own ship’s consumption, route and contracted fuel prices before relying on any payback claim.

See also

• MARPOL Annex VI: parent annex
• MARPOL Convention: top-level treaty
• IMO 2020 sulphur cap: the 0.50% global cap event
• MARPOL Annex VI Regulation 13: NOx Tier I, II, III: companion engine-NOx regulation
• MARPOL Annex VI Regulation 18: Bunker Delivery Note: documentary verification framework
• Baltic Sea SECA + NECA
• North Sea SECA + NECA
• North American ECA
• US Caribbean ECA
• Mediterranean SECA 2025
• Per-fuel WTW: VLSFO/MGO
• Per-fuel WTW: HFO
• Per-fuel WTW: LNG Otto / diesel
• Cylinder oil base number and fuel sulphur
• Helsinki Convention 1992
• Calculator catalogue

References

Related calculators

• MARPOL Annex VI/14 - Sulphur emissions
• MARPOL Annex VI/7 - Duration of certificate
• MARPOL Annex VI/6 - IAPP certificate
• MARPOL Annex VI/5 - Survey and certification
• MARPOL Annex VI/28 - CII
• MARPOL Annex VI/27 - Data collection system
• MARPOL Annex VI/26 - SEEMP revised
• MARPOL Annex VI/25 - EEXI