MARPOL Annex VI

MARPOL Annex VI is the IMO instrument that caps air pollution and greenhouse-gas emissions from ships. It limits sulphur in fuel oil to 0.50% globally (from 1 January 2020) and 0.10% in Emission Control Areas, sets three-tier NOx limits for marine diesel engines, and since 1 January 2023 requires the EEXI design index and the annual CII carbon-intensity rating for ships above 5,000 GT. The 2023 IMO GHG Strategy (Resolution MEPC.377(80)) targets at least 20% absolute GHG reduction by 2030 and net-zero by or around 2050. A proposed new Chapter 5 establishing the GHG Fuel Intensity standard and a global pricing mechanism was approved at MEPC 83 in April 2025 but has not yet been formally adopted; the extraordinary session MEPC/ES.2 in October 2025 adjourned the adoption vote, with reconvening targeted for October 2026.

ECA quick reference

The table below lists every Emission Control Area designated under MARPOL Annex VI as of June 2026.

Background and history

MARPOL 73/78 and the air-pollution gap

The MARPOL Convention was adopted in 1973 and amended by the 1978 Protocol to cover all ship-borne pollution. Its first five annexes regulated oil (Annex I), noxious liquid substances in bulk (Annex II), harmful substances in packaged form (Annex III), sewage (Annex IV) and garbage (Annex V). Air pollution was not addressed in the 1973 text. By the late 1980s the rapid expansion of long-distance shipping, the move to high-sulphur residual fuels following the oil price shocks of the 1970s, and the emergence of measurable health and ecosystem effects from ship-source SOx and NOx had made the air-pollution gap one of the most-discussed deficiencies of the MARPOL framework.

The Marine Environment Protection Committee (MEPC) of the International Maritime Organization first considered air pollution from ships at MEPC 26 in 1988 and, on the recommendation of the IMO Assembly Resolution A.719(17) of 6 November 1991, set in motion the work that would lead to the adoption of Annex VI. The Norwegian, Swedish and Finnish administrations, supported by the European Community, were the principal driving forces in the early years; the United States Environmental Protection Agency (EPA) and the United Kingdom Department of Transport joined the work programme in 1993.

The 1991 Assembly resolution and the 1997 Conference

MEPC drafted a complete text of Annex VI and a parallel Protocol of 1997 to amend MARPOL 73/78 to add the new annex. Both instruments were adopted at an International Conference of the Parties to MARPOL held in London in September 1997. The Conference adopted thirteen resolutions accompanying the Protocol, including the Technical Code on Control of Emissions of Nitrogen Oxides from Marine Diesel Engines (NOx Technical Code 2008, in its later revised form), which is mandatory under Regulation 13 of Annex VI, and the model International Air Pollution Prevention (IAPP) Certificate.

The 1997 Protocol entered into force under the requirement that 15 states representing not less than 50% of world merchant tonnage by gross tonnage accept it. The threshold was reached on 18 May 2004 with Samoa’s accession; entry into force followed twelve months later on 19 May 2005, eight years after adoption. The relatively long gestation period reflects the difficulty of building consensus on a regime that imposes significant costs on engine manufacturers, fuel suppliers and shipowners across the global fleet.

Entry into force and the 2008 amendments

In 2005 the original Annex VI sulphur cap was 4.50% mass by mass globally and 1.50% in the SOx Emission Control Areas (SECAs) defined by Regulation 14. The North Sea SECA had taken effect under the original Annex VI on 11 August 2007 and the Baltic SECA on 19 May 2006. Within months of the original annex coming into force, MEPC began considering far more ambitious reductions, motivated by health-impact studies showing that ship-source PM2.5 was contributing to between 60,000 and 90,000 premature deaths per year worldwide.

The 2008 amendments to Annex VI, adopted by Resolution MEPC.176(58) on 10 October 2008 and entering into force on 1 July 2010, completely rewrote Regulation 13 (NOx) and Regulation 14 (SOx and PM) and substantially restructured the rest of the annex. The principal changes were:

• The global sulphur cap was scheduled to fall from 4.50% to 3.50% in 2012 and to 0.50% in 2020 (subject to a fuel-availability review). The IMO 2020 sulphur cap was confirmed by MEPC 70 in October 2016.
• The ECA sulphur limit was scheduled to fall from 1.50% to 1.00% in 2010 and to 0.10% in 2015.
• A new three-tier NOx engine certification scheme was introduced (Tier I for engines installed on or after 1 January 2000, Tier II for engines installed on or after 1 January 2011, Tier III for engines operating in NOx ECAs and installed on or after 1 January 2016).
• A NOx ECA designation framework was added, allowing coastal states to apply for an area of the sea to be designated for NOx control as well as SOx control.
• Detailed fuel-quality requirements were tightened, with the bunker delivery note (BDN) made mandatory in its current form.

The North American ECA covering the United States and Canadian coastlines was approved by MEPC 59 in July 2009 and entered into force on 1 August 2012; the United States Caribbean Sea ECA followed on 1 January 2014. The Mediterranean Sea Emission Control Area for SOx (Resolution MEPC.361(79)) took effect on 1 May 2025; designation of the same area for NOx is under negotiation with a likely target of 2027. At MEPC 83 in April 2025 the Committee also approved the North-East Atlantic Ocean as a combined SOx+NOx+PM ECA; formal adoption of that designation was adjourned together with the Net-Zero Framework in October 2025.

Energy-efficiency amendments 2011 to 2018

The Annex VI Chapter 4 on energy efficiency was added by Resolution MEPC.203(62) of 15 July 2011, entering into force on 1 January 2013. It was the first mandatory energy-efficiency regulation for any international transport sector. The chapter introduced four operative concepts:

• Attained EEDI (Regulation 20), the design-phase index for new ships of 400 GT and above contracted on or after 1 January 2013. The attained EEDI calculator implements the formula as set out in Resolution MEPC.245(66).
• Required EEDI (Regulation 21), a maximum permissible attained EEDI that varies by ship type, size category and entry-into-service year. The required EEDI calculator implements the reference-line and reduction-factor methodology of Resolution MEPC.231(65).
• Attained EEDI verification process, with the survey calculator implementing the verification cycle and pre-verification protocol.
• SEEMP (Regulation 22), a mandatory ship-specific Ship Energy Efficiency Management Plan for all ships of 400 GT and above. The SEEMP calculator implements the original Part I structure.

A 2014 amendment (Resolution MEPC.232(65)) introduced the EEDI for ro-ro cargo and ro-ro passenger ships. A 2016 amendment (Resolution MEPC.282(70)) introduced the IMO Data Collection System (DCS) by adding Regulation 22A, requiring all ships of 5,000 GT and above engaged on international voyages to report annual fuel consumption data to flag administrations from 1 January 2019. The IMO DCS calculator implements the annual reporting cycle, and the IMO DCS vs EU MRV comparison explains the parallel European reporting regime.

EEXI, CII and the 2021 amendments

The 2021 amendments adopted by Resolution MEPC.328(76) of 17 June 2021 and entering into force on 1 November 2022 added the second-generation operational regime to Chapter 4. The principal new elements were:

• EEXI (Regulation 25), the Energy Efficiency Existing Ship Index, applying to all ships of 400 GT and above engaged on international voyages from the first survey on or after 1 January 2023. The EEXI attained calculator and EEXI required calculator implement the indices; the MARPOL EEXI required calculator provides the regulation-anchored variant.
• SEEMP Part III (Regulation 26), a CII operational plan that the master must implement, requiring documented procedures for monitoring and improving annual operational carbon intensity.
• CII rating (Regulation 28), the Carbon Intensity Indicator, applying to all ships of 5,000 GT and above engaged on international voyages from 1 January 2023. Ships are rated A through E by reference to the required CII for the year and the ship type. The CII attained calculator, CII required calculator and CII rating calculator implement the formulae of Resolution MEPC.336(76) and the rating boundaries of Resolution MEPC.339(76).
• CII corrective action plan (Regulation 28.10), the requirement that a ship rated D for three consecutive years or rated E for one year must produce a written corrective action plan as part of its SEEMP Part III. The CII 3-year corrective action calculator implements the regulation-driven plan-trigger logic.

The reduction factors for EEXI and CII were set at 30% by 2025 (relative to the 2008 reference line) for many ship-type and size categories, with phased increases through 2030. The full reduction trajectory through 2030 was confirmed at MEPC 78 in 2022 and is set out in Resolution MEPC.350(78).

Net-Zero Framework (approved MEPC 83, April 2025; not yet adopted)

At its 83rd session in April 2025, MEPC approved the IMO Net-Zero Framework as a proposed new Chapter 5 of MARPOL Annex VI, comprising the GHG Fuel Intensity (GFI) standard and a global economic instrument. The framework is the first global GHG pricing mechanism proposed for international shipping. Formal adoption was targeted for the extraordinary session MEPC/ES.2 held 14 to 17 October 2025, but that session adjourned without adopting the text after Member States voted 57 to 49 to defer proceedings by one year. Talks are set to reconvene in October 2026; the framework is not yet adopted and not yet in force. Once adopted, the tacit-acceptance procedure means entry into force would follow approximately 16 months later, making 2028 the earliest plausible date. The principal elements of the approved text are:

• GFI standard: every ship of 5,000 GT and above engaged on international voyages must achieve an attained well-to-wake GHG fuel intensity (in g CO₂e per MJ) at or below an annually-tightening Required GFI. The reduction trajectory in the approved text begins in 2028 with a 4% reduction relative to a 2008 well-to-wake baseline, rising to 30% by 2035 and 65% by 2040. The methane slip to CO₂-equivalent calculator and the LNG WtW calculator implement the GFI building blocks.
• Economic instrument: ships exceeding the Required GFI must surrender Remediation Units (RUs) at a price set by IMO. Ships emitting at or below the Direct Compliance Threshold (a stricter intensity than the Required GFI) earn Surplus Units that may be banked or traded. The instrument is conceptually similar to the cap-and-trade design of the EU ETS Maritime but operates on a global, fuel-intensity basis rather than a regional, total-emissions basis.
• Scope and timeline: in the approved text the regime applies to ships of 5,000 GT and above on international voyages from the year following entry into force, with a formal review against the IMO 2023 GHG Strategy checkpoints in 2030.

The LCA Guidelines underpinning the well-to-wake GFI calculation are set out in Resolution MEPC.391(81), adopted 22 March 2024 at MEPC 81, which replaced the earlier MEPC.376(80) guidelines. The Net-Zero Framework, if adopted, would be the most consequential addition to Annex VI since the 2008 amendments; its eventual shape after the 2026 reconvening may differ from the approved April 2025 text.

Structure of Annex VI

Annex VI is currently divided into five chapters containing 25 numbered regulations, supplemented by nine appendices. The chapter structure as in force after the MEPC.328(76) amendments is:

• Chapter 1: General (Regulations 1 to 4)
• Chapter 2: Survey, certification and means of control (Regulations 5 to 11)
• Chapter 3: Requirements for control of emissions from ships (Regulations 12 to 18)
• Chapter 4: Regulations on energy efficiency for ships (Regulations 19 to 23, with Regulations 25 to 28 inserted by the 2021 amendments to cover EEXI, SEEMP Part III, IMO DCS and CII)
• Chapter 5: Verification of compliance with Annex VI (Regulations 39 to 41 in numbering aligned with the corresponding SOLAS Chapter XIII)

The IMO Net-Zero Framework, approved at MEPC 83 in April 2025, proposes a new Chapter 5 (renumbering the existing verification chapter) to house the GHG Fuel Intensity standard and the global economic instrument. Because formal adoption was adjourned at MEPC/ES.2 in October 2025, this additional chapter is not yet part of the binding text; it is covered in the section below on the proposed framework.

The nine appendices are:

• Appendix I: Form of the IAPP Certificate (Regulation 8)
• Appendix II: Test cycles and weighting factors for the NOx Technical Code (Regulation 13)
• Appendix III: Criteria and procedures for designation of Emission Control Areas (Regulation 14, Regulation 13)
• Appendix IV: Type approval and operating limits for shipboard incinerators (Regulation 16)
• Appendix V: Information to be included in the Bunker Delivery Note (Regulation 18.5)
• Appendix VI: Fuel verification procedure for fuel oil samples (Regulation 18.8.2 and 18.8.3)
• Appendix VII: Emission Control Areas (geographic coordinates)
• Appendix VIII: Form of the IEE Certificate (Regulation 8.5)
• Appendix IX: Information to be submitted to the IMO Ship Fuel Oil Consumption Database (Regulation 27)

Chapter 1: General provisions (Regulations 1 to 4)

Regulation 1: Application

Annex VI applies to all ships, except where expressly provided otherwise in Regulations 3, 5, 6, 13, 15, 16, 18, 19, 20, 21, 22, 23, 24, 27 and 28. The annex draws no distinction between ships engaged on international voyages and those engaged exclusively on domestic voyages, although the reporting and verification regime under Chapter 2 and the energy-efficiency regulations of Chapter 4 apply principally to ships of 400 GT or 5,000 GT and above engaged on international voyages.

Regulation 2: Definitions

Regulation 2 defines the working vocabulary of the annex, more than forty terms, including “annual fuel oil consumption”, “associated calorific value”, “attained EEDI” and “attained EEXI”, “auxiliary control device”, “Cf” (the fuel-mass-to-CO₂ conversion factor), “continuous feeding” of incinerators, “DCS”, “Director”, “emission”, “Emission Control Area”, “Emission Control Area not for sulphur and particulate matter” (the NOx ECA category), “energy-efficiency design index”, “energy-efficiency existing ship index”, “fuel oil”, “GHG fuel intensity”, “indispensable”, “installed”, “marine diesel engine”, “MARPOL”, “NOx Technical Code”, “ozone-depleting substances”, “Required EEDI”, “ship”, “shipboard incineration”, “ship type”, “sulphur content of fuel oil” and “tanker”. The 2025 Net-Zero Framework amendments add “Direct Compliance Threshold”, “GFI Surplus Unit”, “GFI Remediation Unit” and “well-to-wake”.

The definition of marine diesel engine is critical to Regulation 13. It includes any reciprocating internal combustion engine operating on liquid or dual fuel, regardless of installation type, but excludes engines used solely for emergency purposes (e.g. emergency generator engines) and propulsion engines on lifeboats. The 2008 amendment to the definition extended Regulation 13 to dual-fuel engines operating in liquid mode.

Regulation 3: Exceptions and exemptions

Regulation 3 exempts emissions necessary for securing the safety of a ship or saving life at sea, emissions resulting from damage to a ship or its equipment provided that all reasonable precautions have been taken after the occurrence of the damage and emissions undertaken with prior approval of the Administration for the purpose of testing or development of emission-reduction technology. Regulation 3.4 also provides for emissions from ships engaged exclusively in voyages within waters subject to the sovereignty or jurisdiction of the state whose flag the ship is entitled to fly, where Annex VI applies as a matter of national law and where the state may exempt such ships from compliance with specific regulations.

Regulation 4: Equivalents

Regulation 4 allows the Administration to authorise any fitting, material, appliance or apparatus to be fitted in a ship as an alternative to that required by Annex VI, provided that the alternative is at least as effective in terms of emissions reduction. Regulation 4.2 requires that the Administration notify the IMO of any such equivalent for circulation to other Parties. The provision provides the legal basis for the use of exhaust gas cleaning systems (EGCS, “scrubbers”) as an equivalent to compliance with the sulphur cap of Regulation 14, and for the use of selective catalytic reduction (SCR) and exhaust gas recirculation (EGR) as equivalent to direct engine modification under Regulation 13. The SOx scrubber NaOH dosing calculator implements the operational chemistry of an open-loop or hybrid scrubber, and the EGR rate for Tier III calculator provides the corresponding combustion analysis for EGR systems.

Chapter 2: Survey, certification and means of control (Regulations 5 to 11)

Regulation 5: Surveys

Regulation 5 establishes the survey regime applicable to ships subject to Annex VI. Ships of 400 GT and above engaged on international voyages and fixed and floating drilling rigs and other platforms shall be subject to the surveys specified below, carried out by officers of the Administration or by a Recognised Organisation acting on its behalf:

• Initial survey before the ship is put in service or before the IAPP Certificate is issued for the first time.
• Renewal survey at intervals not exceeding five years.
• Intermediate survey within three months before or after the second anniversary date or within three months before or after the third anniversary date of the IAPP Certificate.
• Annual survey within three months before or after each anniversary date of the IAPP Certificate.
• Additional survey after a repair, alteration or modification that materially affects the equipment, fittings, arrangements or material covered by the annex.

The survey calculator implements the survey-cycle logic for a given ship category, IAPP issue date and class. The Harmonised System of Survey and Certification (HSSC) aligns the Annex VI survey cycle with the SOLAS and International Load Line Convention cycles so that all major certificates can be renewed together.

Regulation 6: Issue or endorsement of certificates

The IAPP Certificate is issued for any ship subject to Annex VI surveys following an initial survey or renewal survey and shall be valid for a period not exceeding five years. The certificate is endorsed at each annual and intermediate survey. Following the 2008 amendments, an EIAPP Certificate (Engine International Air Pollution Prevention Certificate) is issued for each marine diesel engine of more than 130 kW output following the engine’s pre-installation type-approval test under the NOx Technical Code. The IAPP certificate calculator implements the IAPP issue and endorsement logic.

The 2011 Chapter 4 amendments introduced the IEE Certificate (International Energy Efficiency Certificate) under Regulation 8.5, issued following verification that the ship complies with the EEDI, EEXI and SEEMP requirements as applicable. The IEE Certificate is permanently valid (not subject to renewal) but must be re-issued if the ship undergoes major modifications affecting its energy efficiency.

Regulation 7: Issue or endorsement of a certificate by another Government

Where a Government issues an IAPP Certificate, EIAPP Certificate or IEE Certificate at the request of the Administration of another Party, that certificate has the same force as if issued by the requesting Administration. The provision facilitates flag-state delegation to coastal Recognised Organisations and is an extension of the analogous provision under SOLAS Regulation I/8. The duration of certificate calculator implements the validity rules.

Regulation 8: Form of certificates

Regulation 8 prescribes the form of the IAPP, EIAPP and IEE certificates as set out in Appendices I, IV and VIII respectively. The certificates record the ship particulars, the dates of survey, the limits to which the ship is certified (e.g. the sulphur limit at which the ship operates, the EEDI value, the EEXI value, and the CII rating record from Regulation 28).

Regulation 9: Duration and validity of certificates

A certificate is invalid if the ship undergoes modifications that materially affect compliance, if the ship changes flag, or if the renewal survey is not completed within the prescribed period. Regulation 9 also provides for short extensions of validity (up to three months) to allow a ship to complete the voyage to the port at which it is to be surveyed. The IEE Certificate is exempted from the validity-extension provisions because it is not subject to renewal.

Regulation 10: Port state control on operational requirements

A ship in a port or offshore terminal of another Party is subject to inspection by officers duly authorised by that Party for the purpose of verifying that the master and crew are familiar with essential shipboard procedures relating to the prevention of air pollution. Where there are clear grounds for believing that the master or crew are not familiar with essential procedures, the ship may be inspected in detail under the port state control regime. The port state control NOx calculator implements the inspection-targeting logic for the Paris MOU, Tokyo MOU and the United States Coast Guard.

Regulation 11: Detection of violations and enforcement of Annex VI

Parties cooperate in the detection of violations and the enforcement of Annex VI. A ship in any port or offshore terminal of a Party is subject to inspection by officers of that Party. The provision is the legal basis for in-port fuel sampling and for the analysis of fuel samples to verify compliance with the sulphur and quality requirements of Regulations 14 and 18. The fuel oil sampling calculator implements the sampling and chain-of-custody requirements.

Chapter 3: Requirements for control of emissions from ships (Regulations 12 to 18)

Regulation 12: Ozone-depleting substances

Regulation 12 prohibits the deliberate emission of ozone-depleting substances; the Regulation 12 ozone-depleting substances article treats the phase-out schedule and the ODS Record Book in full. New installations containing chlorofluorocarbons (CFCs) and halons were prohibited from 19 May 2005, and new installations containing hydrochlorofluorocarbons (HCFCs) were prohibited from 1 January 2020. Existing installations are subject to a controlled phase-out and to mandatory record-keeping in the Ozone-Depleting Substances Record Book required by Regulation 12.6.

The substances regulated under Regulation 12 are listed in the Montreal Protocol on Substances that Deplete the Ozone Layer (1987) as amended; the IMO regulation provides the implementing mechanism for ships. The ozone-depleting substances phase-out calculator and the ODS calculator implement the inventory and phase-out checks. The principal substance still in active use on ships in the late 2020s is HCFC-22 (R-22) in older refrigeration and air-conditioning installations.

Regulation 13: Nitrogen oxides

Regulation 13 establishes the engine-certification regime for marine diesel engines of more than 130 kW power output; the Regulation 13 NOx Tier I/II/III article sets out the tier curves, the ECA geography and the SCR/EGR compliance routes in detail. The regulation prescribes maximum NOx emission limits in g/kWh as a function of the engine’s rated speed n (in rpm). The three tiers and their applicability dates are:

The Tier II NOx limit calculator and the Tier III NOx limit calculator implement the rated-speed-dependent limits. Tier III applies to engines installed on or after 1 January 2016 on ships operating in a designated NOx ECA. The North American ECA was the first NOx ECA to take effect under Tier III on 1 January 2016, followed by the United States Caribbean Sea ECA (1 January 2016), the Baltic Sea NOx ECA (1 January 2021) and the North Sea NOx ECA (1 January 2021). The Mediterranean NOx ECA is under negotiation with a likely entry-into-force date of 2027.

The principal compliance technologies for Tier III are selective catalytic reduction (SCR) and exhaust gas recirculation (EGR), both used in combination with low-NOx engine combustion strategies. SCR uses a urea injection followed by a catalytic converter to reduce NOx to N₂; EGR re-introduces a portion of the exhaust gas into the combustion chamber to lower the peak combustion temperature and inhibit thermal NOx formation through the Zeldovich mechanism. LNG dual-fuel engines operating in gas mode (Otto cycle) achieve Tier III compliance directly through low-temperature combustion without after-treatment, although they then face the issue of methane slip discussed below. The EGR rate for Tier III calculator implements the EGR rate-of-recirculation analysis.

The NOx Technical Code 2008 (NTC 2008), made mandatory by Regulation 13, prescribes the test procedures (the E2, E3 or D2 test cycles for different engine applications), the on-board verification procedures, and the calculation of the weighted average NOx emission. Engines are tested on the manufacturer’s test bed in the certification phase, recorded in the EIAPP Certificate, and verified on-board by the parameter-check method (verification that the engine’s adjustable components, settings and operating parameters are within the EIAPP envelope) or, where required, the simplified measurement method using a portable emission measurement system.

The Norway NOx Fund levy calculator implements the parallel national NOx pricing scheme operating in Norwegian waters, which complements the Annex VI Tier III ECA framework with a market-based instrument.

Regulation 14: Sulphur oxides and particulate matter

Regulation 14 establishes the maximum sulphur content of any fuel oil used on board ships; the Regulation 14 sulphur cap article covers the 0.50% global cap, the 0.10% ECA cap, scrubbers as an equivalent and the FONAR procedure at length. The limits as currently in force are:

• Global cap: 0.50% mass by mass (m/m) sulphur, in force from 1 January 2020.
• ECA cap: 0.10% m/m sulphur, in force in all designated SOx ECAs from 1 January 2015.

The Regulation 14 sulphur calculator and the SOx from fuel sulphur calculator implement the sulphur-content checks and the corresponding SOx emission rate.

The IMO 2020 sulphur cap is the most-discussed of the Regulation 14 limits, having reduced ship-source SOx emissions globally by approximately 75% in 2020 according to the IMO Fourth GHG Study. The cap drove a major restructuring of the bunker market, with the transition from heavy fuel oil (HFO) to very-low-sulphur fuel oil (VLSFO) and to ECA-compliant marine gas oil (MGO) blends.

The principal compliance options under Regulation 14 are:

• Compliant fuel (VLSFO or MGO) burned in the existing engine without modification.
• Exhaust gas cleaning system (EGCS or “scrubber”) as an equivalent under Regulation 4.1, removing SOx from the exhaust gas to a level equivalent to the use of compliant fuel. Open-loop scrubbers discharge the wash water to sea (subject to discharge water quality requirements); closed-loop scrubbers retain the wash water for shore disposal; hybrid scrubbers can switch between modes. The SOx scrubber NaOH dosing calculator implements the operational chemistry.
• Alternative fuels that are inherently below the sulphur limit, including LNG, methanol, ammonia and biofuels.

The Fuel Oil Non-Availability Report (FONAR) procedure under Regulation 18.2 allows a ship to use non-compliant fuel where compliant fuel is genuinely unavailable. The FONAR calculator implements the documentary record. FONAR is intended as a short-term contingency, not a routine compliance pathway, and the master must demonstrate good-faith effort to procure compliant fuel.

Regulation 14 also addresses particulate matter. The 0.50% sulphur cap reduces PM emissions by approximately 50% by mass; the PM10 and PM2.5 calculator implements the secondary-PM and primary-PM mass calculation from a given fuel sulphur content and engine load. The filter smoke number to black carbon calculator provides the FSN-to-BC conversion used in low-load engine particulate analysis. The black carbon calculator implements the IMO-recommended Black Carbon Reference Method, which is being developed for inclusion in a future Annex VI amendment specifically targeting Arctic shipping under MEPC 80 (2023) recommendations.

Regulation 15: Volatile organic compounds

Regulation 15 controls VOC emissions from tankers carrying crude oil; the Regulation 15 VOC emissions article details the VOC Management Plan and the vapour-recovery arrangements. The regulation requires that ports designated by Parties to control such emissions provide vapour collection systems and that tankers fitted with the corresponding shore-connection equipment use them. A VOC Management Plan is mandatory for crude oil tankers under Regulation 15.6. The VOC management calculator implements the management-plan compliance check, and the crude tanker VOC calculator implements the loading-emission estimate. The VOC Reg 15 calculator provides the regulation-anchored variant.

The principal sources of VOC from tanker operations are loading displacement (vapour displaced from the cargo tank as cargo is loaded) and breathing losses (vapour expelled by daily temperature and pressure variations during the voyage). Loading displacement is by far the larger source, and the standard mitigation is the connection of a vapour collection arm to the shore terminal at the loading berth.

Regulation 16: Shipboard incineration

Regulation 16 prescribes the operating standards for shipboard incinerators installed on or after 1 January 2000; the Regulation 16 shipboard incineration article covers the prohibited-material list, the 850°C outlet temperature and the Appendix IV type-approval regime. Materials prohibited from shipboard incineration include polychlorinated biphenyls (PCBs), garbage containing more than traces of heavy metals, refined petroleum products containing halogen compounds, sewage sludge and sludge oil that are not generated on board, and exhaust gas cleaning system residues. The shipboard incinerator capacity calculator implements the throughput-rate verification, and the Reg 16 calculator provides the regulation-anchored compliance check.

The minimum exhaust gas temperature at the incinerator outlet is 850°C with O₂ in the combustion chamber at not less than 6%, with continuous monitoring of the combustion temperature and the gas-phase residence time. Approved incinerator designs are listed in Appendix IV.

Regulation 17: Reception facilities

Regulation 17 requires Parties to ensure the provision of adequate facilities at ports and terminals for Annex VI wastes; the Regulation 17 reception facilities article sets out the scope of those facilities and the parallel duties under the other MARPOL annexes. The reception requirement covers ozone-depleting substances and equipment containing such substances when removed from ships, exhaust gas cleaning system residues, and used fuel oil and other Annex VI-related wastes. The provision parallels the reception-facility requirements of MARPOL Annex I (oil), Annex II (NLS) and Annex IV (sewage), and the Annex V garbage reception facilities calculator.

Regulation 18: Fuel oil availability and quality

Regulation 18 sets out the fuel-oil quality and documentary requirements that govern bunker supply globally; the Regulation 18 bunker delivery note and fuel quality article treats the BDN, the retained MARPOL sample and the Appendix VI verification procedure in full. The principal requirements are:

• Fuel oil for combustion purposes shall be a blend of hydrocarbons derived from petroleum refining, although small amounts of additives intended to improve some aspects of performance are permitted.
• The fuel shall be free from inorganic acid, free from any added substance or chemical waste that jeopardises the safety of ships or adversely affects the performance of machinery, or is harmful to personnel, or contributes to additional air pollution.
• The fuel shall meet the sulphur limit applicable to the area of operation under Regulation 14.

Bunker supply is documented by the Bunker Delivery Note (BDN), the form of which is prescribed in Appendix V. Each BDN must be retained on board for not less than three years and is subject to inspection by port state control. A representative sample of the fuel oil delivered is sealed and signed by the supplier’s representative and the master and retained on board for not less than 12 months. The BDN calculator implements the documentary check, and the BDN reconciliation calculator implements the operational reconciliation against on-board fuel records.

The fuel verification procedure of Appendix VI applies when port state control or an Administration tests the retained MARPOL sample (not the supplier’s commercial sample) and the result exceeds the sulphur limit by more than the laboratory test tolerance. The bunker quality dispute calculator implements the test variance and dispute escalation logic. Regulation 18 has been the subject of intense litigation and arbitration over the years, particularly in disputes between bunker suppliers and shipowners about the integrity of bunker samples and the validity of laboratory test results.

The 2018 amendments to Regulation 18 introduced the prohibition on the carriage of non-compliant fuel oil for use on board ships, with the limited exception of fuel oil intended for delivery to other ships. The amendment, in force from 1 March 2020, was a critical anti-evasion measure for the IMO 2020 sulphur cap, removing the ability of a ship to claim that high-sulphur fuel on board was for “future delivery to a non-Party” or for storage purposes.

Chapter 4: Energy efficiency for ships (Regulations 19 to 23 and 25 to 28)

Chapter 4 was added by Resolution MEPC.203(62) of 15 July 2011, entering into force on 1 January 2013, and substantially expanded by Resolutions MEPC.328(76) (2021) and MEPC.350(78) (2022). It is divided functionally into the EEDI regime for new ships (Regulations 19 to 21), the SEEMP regime for all ships (Regulation 22), the IMO DCS reporting regime (Regulations 22A and 27), the EEXI regime for existing ships (Regulation 25), the SEEMP Part III CII operational plan (Regulation 26) and the CII rating system (Regulation 28).

Regulations 19 to 21: EEDI for new ships

Regulation 19 prescribes the application of the EEDI to ships of 400 GT and above contracted for construction on or after 1 January 2013, with a delivery date on or after 1 July 2015. The ship types covered are bulk carriers, gas carriers, tankers, container ships, general cargo ships, refrigerated cargo carriers, combination carriers, ro-ro cargo ships, ro-ro passenger ships, ro-ro vehicle carriers, LNG carriers and cruise passenger ships with non-conventional propulsion (the latter two added in 2014).

Regulation 20 requires the attained EEDI to be calculated for each ship covered by Regulation 19 and to be recorded in the IEE Certificate. The attained EEDI is the design-phase ratio of the ship’s CO₂ emissions per unit of transport work, formulated as a quotient with the sum of CO₂ emissions from the main engines, auxiliary engines and any other power consumers in the numerator and the product of the design capacity (deadweight or gross tonnage depending on ship type) and the reference speed in the denominator. The attained EEDI calculator implements the formula of Resolution MEPC.245(66), and the attained-vs-required EEDI calculator compares the attained value against the regulation-driven Required EEDI.

Regulation 21 prescribes the Required EEDI, the maximum permissible attained EEDI for the ship type and size category. The required value is calculated from the EEDI reference line for the ship type (Resolution MEPC.231(65)) reduced by the applicable phase reduction factor:

• Phase 0: from 1 January 2013, no reduction (compliance with the reference line itself).
• Phase 1: from 1 January 2015, 10% reduction.
• Phase 2: from 1 January 2020, 20% reduction.
• Phase 3: from 1 April 2022 (advanced from 1 January 2025) for larger ships, 30% reduction.

The required EEDI calculator, the reference-line calculator and the phase factor calculator implement the components of the Required EEDI. The innovative technology calculator implements the EEDI credit for innovative energy-efficient technologies under Resolution MEPC.244(66). The ice-class fj calculator implements the ice-class correction factor fj of Regulation 21.5; the fcubic calculator implements the fcubic form correction; and the fvse calculator implements the fVSE voluntary structural enhancement correction.

Regulation 22: SEEMP

Regulation 22 requires every ship of 400 GT and above to keep on board a Ship Energy Efficiency Management Plan (SEEMP), specific to the ship and approved by the Administration. The SEEMP is a four-step plan covering planning, implementation, monitoring and self-evaluation of energy-efficiency measures.

Following the 2021 amendments, the SEEMP is divided into three parts:

• SEEMP Part I: the original ship-specific energy management plan covering technical and operational measures (Regulation 22.1).
• SEEMP Part II: the ship-specific data collection plan for the IMO DCS, replacing the earlier separate data-collection-plan requirement under Regulation 22A (Regulation 22.2).
• SEEMP Part III: the ship-specific CII operational plan including a target attained CII for each calendar year, an implementation plan, a self-evaluation procedure and, where applicable, a corrective action plan (Regulation 26).

The SEEMP calculator implements the original Part I structure, and the SEEMP revised calculator implements the post-2021 Part III structure. SEEMP Part III is approved by the Administration or its Recognised Organisation and is subject to verification at each annual survey under Chapter 2.

Regulations 22A and 27: IMO Data Collection System

Regulation 22A (now relocated to Regulation 27 in the 2021-renumbered text) prescribes the IMO Data Collection System (DCS). Every ship of 5,000 GT and above engaged on international voyages shall report annually to its flag Administration the data set out in Appendix IX of the annex, including:

• IMO number (unique ship identifier).
• Period covered (calendar year, 1 January to 31 December).
• Ship-type-specific transport-work parameters (deadweight, capacity, distance travelled, hours under way).
• Fuel oil consumption by fuel type, in metric tonnes.
• Other data including methods of fuel consumption measurement, EEDI value (where applicable) and ice class.

Flag Administrations transfer the validated data to the IMO Ship Fuel Oil Consumption Database, where it is anonymised and aggregated for the annual IMO Fuel Oil Consumption Report to MEPC. The IMO DCS report calculator implements the annual reporting cycle, and the DCS calculator provides the regulation-anchored variant. The IMO DCS vs EU MRV comparison explains the parallel European reporting regime that has run since 2018 and is in many ways the IMO DCS’s regional analogue.

Regulation 23: Promotion of technical co-operation

Regulation 23 obliges Parties to provide, through the IMO, technical assistance to developing countries in the implementation of the Annex VI energy-efficiency requirements. The transfer of efficiency tech calculator implements the inventory of technologies covered by the regulation. Implementation has been carried out principally through the IMO GHG SMART Container Programme and the GreenVoyage 2050 Project, both administered by the IMO Technical Co-operation Division.

Regulation 25: EEXI

Regulation 25 applies the EEXI to all ships of 400 GT and above engaged on international voyages from the first IAPP renewal survey on or after 1 January 2023. The EEXI follows the same formula as the EEDI but is calculated for the ship as built rather than the ship as designed; the principal differences are that the SFOC is taken from the EIAPP Certificate (or default values) rather than from the engine’s shop test, and the reference speed is the ship’s speed at 75% of MCR (with optional Engine Power Limitation, EPL, used to reduce MCR and therefore reduce attained EEXI).

The attained EEXI calculator, required EEXI calculator and the MARPOL EEXI required calculator implement the regulation. The EEXI Reg 25 calculator provides the regulation-anchored variant. The reduction factors applied to the EEDI reference line to derive the Required EEXI are 20% for most categories, with 30% for some larger sub-categories, applying immediately rather than progressively. The principal compliance lever for existing ships unable to meet the Required EEXI without modification is Engine Power Limitation (EPL), a permanent or sealable mechanical or software limitation of the maximum continuous engine output that reduces the attained EEXI proportionally. The SFOC sensitivity to air temperature calculator implements the engine performance correction relevant to the EEXI verification.

Regulation 26: SEEMP revised (CII operational plan)

Regulation 26 requires the master to implement the ship-specific SEEMP Part III, the CII operational plan, on a calendar-year basis. The plan must include a target attained CII for each calendar year, an implementation plan describing the actions to be taken to achieve the target, and a self-evaluation procedure. The Administration verifies SEEMP Part III at each annual survey and confirms that the implementation matches the plan.

Where a ship is rated D for three consecutive years or E for one year under Regulation 28, the master must produce a corrective action plan as part of the next annual SEEMP Part III review. The CII 3-year corrective action plan calculator implements the trigger logic and the structure of the corrective action plan as specified in MEPC Circular MEPC.7/Circ.16.

Regulation 28: CII rating

Regulation 28 prescribes the Carbon Intensity Indicator (CII) for all ships of 5,000 GT and above engaged on international voyages from 1 January 2023. Each ship’s attained operational CII is calculated annually as:

CII attained = total annual mass of CO₂ ÷ (transport work)

where the transport work is the product of deadweight (DWT) and distance travelled (in nautical miles) for cargo ships, with ship-type-specific corrections set out in Resolution MEPC.336(76). The CII attained calculator, CII required calculator, CII rating calculator and CII voyage adjustment calculator implement the components of the framework. The CII Reg 28 calculator provides the regulation-anchored variant.

The attained CII is compared against the Required CII for the ship type and year (Resolution MEPC.339(76)), and the ship is given a rating from A (major superior) to E (inferior) based on the boundaries (the d vector) defined in MEPC.339(76). The reduction trajectory of the Required CII is 5% per year between 2023 and 2026, with the trajectory beyond 2026 to be reviewed at MEPC 86 in 2027. The CII year-on-year improvement calculator implements the year-on-year reduction analysis.

The SFOC-to-CII converter calculator explicitly links engine SFOC to the ship’s annual CII rating, demonstrating that an engine SFOC improvement of approximately 1 g/kWh translates into an annual CII improvement of approximately 0.5%. The slow steaming and CII article explains the principal operational lever, the cubic relationship between speed and fuel consumption, so that a 10% speed cut reduces propulsion power and fuel burn by roughly 27%, with a proportionate effect on CII.

Proposed Chapter 5: Net-Zero Framework (approved MEPC 83, April 2025; adoption adjourned)

The Net-Zero Framework approved at MEPC 83 in April 2025 proposes a new Chapter 5 of Annex VI comprising the GHG Fuel Intensity (GFI) standard and a global economic instrument. It’s the first global GHG pricing mechanism proposed for international shipping. Formal adoption was adjourned at the extraordinary session MEPC/ES.2 in October 2025; the framework is not yet part of the binding text. The principal elements of the approved text are:

GHG Fuel Intensity (GFI) standard

The attained GFI is the well-to-wake (WtW) GHG intensity of the fuel mix consumed by the ship in the calendar year, expressed in g CO₂-equivalent per MJ. The well-to-wake basis includes all upstream emissions (fuel production, refining and transport), all combustion emissions (CO₂, CH₄ and N₂O converted to CO₂-equivalent using the GWP100 metric), and any methane slip from incomplete combustion in dual-fuel engines. The methane slip CO₂-equivalent calculator and the LNG WtW calculator implement the GFI building blocks.

The Required GFI is set annually and reduces from the 2008 well-to-wake baseline by 4% in 2028, 17% in 2030, 30% in 2035 and 65% in 2040. A second Direct Compliance Threshold (DCT) is set tighter than the Required GFI; ships achieving an attained GFI at or below the DCT earn surplus units.

Economic instrument

Ships exceeding the Required GFI must surrender Remediation Units (RUs) at a price set by IMO under the Net-Zero Framework. The price is reviewed periodically and is set initially at approximately USD 100 per tonne CO₂-equivalent in the 2027 implementation year, rising on a defined trajectory. Ships emitting at or below the DCT earn Surplus Units (SUs), which may be banked for future use or traded to other ships in deficit. The ship’s annual position (units earned, units required, units surrendered) is reported to the IMO Secretariat through the IMO DCS reporting infrastructure, with the IMO Net-Zero Fund acting as the central repository for RU sales revenue.

Phase-in and timeline uncertainty

In the approved text the regime applies first to ships of 5,000 GT and above on international voyages from the year following entry into force (originally projected as 1 January 2027, now uncertain given the MEPC/ES.2 adjournment). Reduction factors and the price of RUs are subject to review in 2030 against the IMO 2023 GHG Strategy checkpoints. A formal review of the regime is planned for MEPC 92 in 2031. The exact entry-into-force date will only become known after formal adoption, which is now targeted for October 2026.

Interaction with regional regimes

The Net-Zero Framework is designed to interact with rather than displace regional regimes such as the EU ETS Maritime, FuelEU Maritime, the UK ETS for shipping and the California At-Berth Rule. Ships operating in multiple jurisdictions are subject to the Net-Zero Framework on a global basis and to regional regimes on the share of voyages within those regions. A “double-counting” avoidance mechanism is under negotiation, with the working assumption that compliance with one regime does not automatically discharge the obligation under the other but that the marginal cost is reduced through the sharing of fuel-decarbonisation infrastructure investment.

The MARPOL EU ETS cost calculator and the MARPOL FuelEU penalty calculator implement the European-side analogues that ships are managing in parallel with the IMO Net-Zero Framework.

Chapter 5: Verification of compliance with Annex VI

Chapter 5 (Regulations 39 to 41 in the post-2018 numbering) was added by Resolution MEPC.296(72) of 13 April 2018 and aligned with the parallel verification chapters of SOLAS Chapter XIII and MARPOL Annex VI Chapter 5. The chapter requires Parties to comply with the III Code (the IMO Instruments Implementation Code) and to be subject to mandatory IMO Member State Audit Scheme (IMSAS) audits. Verification of compliance covers the flag state’s implementation and enforcement of all regulations in Annex VI, including survey integrity, certificate validity, port state control performance, and reporting under the IMO DCS and, once in force, the Net-Zero Framework.

Implementation and enforcement

Flag state surveys

Flag state Administrations, or Recognised Organisations (typically classification societies acting under formal authorisation) carry out the survey programme prescribed by Chapter 2. The IACS Common Structural Rules and Common Survey Rules harmonise the survey procedures across the major class societies, ensuring consistent application of Annex VI regardless of flag.

Port state control regimes

Port state control inspects compliance with Annex VI under the regional MOU regimes:

• Paris MOU (Europe and the North Atlantic) operates the NOx PSC initiative under which inspectors check engine-room logs, EIAPP certificates, fuel-changeover records and bunker delivery notes. The 2018 Concentrated Inspection Campaign (CIC) on Annex VI compliance found compliance failures on approximately 15% of inspected ships, predominantly relating to BDN documentation and SEEMP implementation.
• Tokyo MOU (Asia-Pacific) operates a parallel initiative.
• The United States Coast Guard enforces Annex VI under 33 CFR Part 401, with detention powers used regularly against ships found to have used non-compliant fuel within the United States ECA without a valid FONAR.

Sanctions

Sanctions for Annex VI violations are imposed by the flag state and, for violations committed within port-state jurisdiction, by the port state. Typical port-state sanctions for sulphur-cap violations include detention, financial penalty (often calculated as a multiple of the compliance fuel cost saved) and, in repeat-offender cases, banning from the relevant regional waters. The Paris MOU “white, grey and black list” tracks flag-state performance; ships flagged in black-list states are subject to enhanced inspection rates.

Compliance economics

The compliance economics of Annex VI are dominated by the fuel-cost differential between compliant and non-compliant fuels. In the period immediately following 1 January 2020, the price differential between heavy fuel oil (HFO) and very-low-sulphur fuel oil (VLSFO) reached a peak of approximately USD 350 per tonne, declining to a more typical range of USD 100 to USD 200 per tonne by 2023. The differential supports the business case for scrubber installations for ships with high annual fuel consumption and a long expected service life; for shorter-life or lower-consumption ships, fuel-switching to VLSFO has been the dominant compliance pathway.

The economics of Tier III NOx compliance are similarly dominated by the cost of SCR installation and urea consumption, with typical SCR retrofit cost of USD 1.5 million to USD 4 million per engine and urea consumption of approximately 5% to 10% of fuel consumption by mass. EGR retrofit cost is generally lower (USD 1 million to USD 2 million per engine) but requires more frequent maintenance.

The CII / EEXI compliance economics are typically dominated by the cost of EPL and operational measures (slow steaming, weather routing, hull cleaning). EPL cost is typically USD 50,000 to USD 250,000 per engine; the corresponding loss of speed capability has commercial consequences for charter rates and turn-around time that vary by trade pattern.

The Net-Zero Framework, if adopted and in force (earliest 2028 given the October 2025 adjournment), will introduce a new cost layer. At an initial RU price of USD 100 per tonne CO₂-equivalent and a typical bulk carrier annual fuel consumption of 10,000 tonnes, the marginal cost of being 1 g CO₂-eq/MJ above the Required GFI is approximately USD 50,000 per year; for a ship 10 g CO₂-eq/MJ above the Required GFI, the cost is approximately USD 500,000 per year. These figures rise approximately linearly with the RU price and approximately linearly with ship fuel consumption. The compliance lever is fuel switching to lower-WtW-intensity alternatives, with LNG (after methane-slip correction) approximately 20% lower than HFO, biofuels typically 70% to 90% lower depending on feedstock, and green methanol, ammonia and hydrogen close to or at zero WtW.

Interaction with regional regimes

Annex VI is the global regulatory baseline. Several regional regimes apply on top of, or in parallel with, the IMO framework:

• EU ETS Maritime (Directive (EU) 2023/959) brings shipping emissions into the EU Emissions Trading System from 1 January 2024 with a phase-in over 2024 to 2026. Ships of 5,000 GT and above must surrender EU Allowances (EUAs) for a percentage of their CO₂ emissions on intra-EU voyages and 50% of CO₂ on voyages between an EU port and a non-EU port. Methane and N₂O are added from 1 January 2026. See the EU ETS for shipping article.
• FuelEU Maritime (Regulation (EU) 2023/1805) imposes a separate well-to-wake GHG intensity requirement on the energy used on board ships calling at EU ports, with reduction factors of 2% (2025), 6% (2030), 14.5% (2035), 31% (2040), 62% (2045) and 80% (2050). See the FuelEU Maritime article and the FuelEU penalties and pooling article.
• California At-Berth Rule (CARB Regulation, 17 CCR §93118.3) requires container, refrigerated cargo, cruise, ro-ro and tanker vessels at California ports to use shore power or an equivalent technology for at least 80% of port time, rising to 90% by 2027.
• UK ETS for shipping is under consultation as of 2025, with a likely entry into force in 2027 covering UK domestic and intra-UK voyages.
• China DCS parallels the IMO DCS and the EU MRV with a separate national reporting regime.
• Norway NOx Fund provides a market-based instrument for NOx emissions in Norwegian waters; ships paying into the fund obtain financial support for NOx-reduction projects. The Norway NOx Fund calculator implements the levy.
• Environmental Ship Index (ESI) is a voluntary index recognised by approximately 50 ports worldwide that grants port-fee discounts to ships scoring above defined thresholds for SOx, NOx and CO₂. The ESI score calculator implements the standard scoring formula.

The interaction between Annex VI and these regional regimes is in many cases additive: a ship trading on intra-EU routes is subject to Annex VI globally, EU ETS Maritime within EU waters, FuelEU Maritime on its EU port calls, and a national NOx Fund or shore-power requirement at specific ports. The compliance burden has pushed fleet management toward integrated regulatory accounting, with many large operators now running single-source compliance teams covering all regimes.

Limitations

This article is the overview of Annex VI as a whole. It is not a substitute for the consolidated text, and several caveats apply to anyone using it operationally.

The annex is amended at almost every MEPC session, and the dates and reduction factors quoted here track the position after the MEPC 83 approval in April 2025. The Net-Zero Framework figures (the 4% to 65% Required GFI trajectory in the approved text, the approximately USD 100 per tonne CO₂-equivalent opening Remediation Unit price, the 2027 or later entry into force) are taken from the approval document. Formal adoption was adjourned at the extraordinary session MEPC/ES.2 in October 2025 and is now targeted for October 2026; the framework is not yet binding law and its final shape may differ from the April 2025 approved text. The surrender price is reviewed periodically rather than fixed, and the entry-into-force date cannot be confirmed until the adoption resolution passes. Always verify against the then-current consolidated MARPOL Annex VI text before operational use.

The regulation numbering is not stable across editions. The 2021 amendments renumbered the energy-efficiency regulations, so Regulation 22A in the older numbering corresponds to Regulation 27 in the consolidated text, and the verification chapter regulations cited here as 39 to 41 align with the parallel SOLAS Chapter XIII numbering. When citing a regulation for an audit or a port-state-control defence, confirm the number against the edition in force at the ship’s flag administration.

The compliance-cost figures (the USD 100 to USD 200 per tonne HFO-to-VLSFO spread, the USD 1.5 million to USD 4 million SCR retrofit, the USD 50,000 to USD 250,000 EPL cost) are market ranges from 2020 to 2025 and move with fuel prices, yard rates and the RU price. Treat them as orders of magnitude for screening, not as a quotation. The NOx tier limits, the sulphur caps and the survey intervals are exact regulatory values and are not subject to that caveat.

Designation of Emission Control Areas is a moving target. The Mediterranean SOx ECA took effect on 1 May 2025; the corresponding Mediterranean NOx ECA was still in negotiation at the time of writing, with 2027 the working target. Always verify ECA boundaries and effective dates against Appendix VII and the relevant MEPC resolution before planning a fuel-changeover or a Tier III routing decision.

The calculators linked from this article implement the operative formulae of the named resolutions, but a calculator output is an estimate for planning. The certified attained EEDI, EEXI and CII values are those recorded on the IEE Certificate and in the SEEMP Part III after verification by the Administration or its Recognised Organisation; where a calculator result and a certified value differ, the certified value governs.

Future outlook

The principal regulatory developments expected through 2030 are:

• Mediterranean NOx ECA entry into force, expected 2027 or later.
• North-East Atlantic ECA (SOx + NOx + PM, approved MEPC 83): formal adoption targeted for October 2026 extraordinary session (was adjourned with the Net-Zero Framework in October 2025).
• Net-Zero Framework formal adoption at the reconvened extraordinary session in October 2026, with entry into force approximately 16 months later (earliest 2028).
• Reduction factor review for the CII trajectory beyond 2026, scheduled for MEPC 86 (2027).
• Black Carbon regulation for Arctic shipping, building on the MEPC 80 (2023) recommendation and the work of the Sub-Committee on Pollution Prevention and Response (PPR).
• MASS-related amendments to Annex VI to accommodate Maritime Autonomous Surface Ships, in parallel with the goal-based MASS Code under negotiation in the COLREGs / SOLAS framework. See the COLREGs Convention article for the parallel work.
• Mid-term review of the Net-Zero Framework at MEPC 92 (2031), with a likely tightening of reduction factors to align with the 2050 net-zero target.

By 2030, Annex VI will have been amended at least three times since the 2025 Net-Zero Framework approval, and the cumulative compliance burden on a typical bulk carrier will be approximately USD 5 million per year in fuel-cost premium and pricing-instrument surrender. By 2040 the equivalent figure is projected at USD 15 million to USD 30 million per year, with the principal driver being the GFI compliance gap as conventional fuels are progressively priced out of the cheapest compliance options.

See also

• MARPOL Convention - the parent treaty of which Annex VI is part
• SOLAS Convention - the principal IMO safety treaty interacting with Annex VI on energy efficiency
• STCW Convention - the training and watchkeeping standards including the Annex VI compliance competencies
• IMO 2020 sulphur cap - the Regulation 14 amendment that took effect on 1 January 2020
• What is CII - the carbon intensity indicator under Regulation 28
• What is EEDI - the energy efficiency design index under Regulations 19 to 21
• What is EEXI - the energy efficiency existing ship index under Regulation 25
• Slow steaming and CII - operational lever for CII compliance
• EU ETS for shipping - the regional cap-and-trade regime running in parallel with Annex VI
• FuelEU Maritime explained - the regional well-to-wake intensity regime
• FuelEU penalties, pooling and multipliers - the FuelEU compliance levers
• IMO DCS vs EU MRV - parallel reporting regimes
• Cold ironing and shore power - in-port emission reduction technique
• Biofuels in shipping - low-carbon fuels for Annex VI compliance
• LNG as marine fuel - dual-fuel pathway for Annex VI compliance
• Methanol as marine fuel - alternative fuel pathway for Annex VI compliance
• Ammonia as marine fuel - zero-carbon fuel pathway for Annex VI compliance
• Heavy fuel oil - the residual fuel that the sulphur cap restricts
• Marine gas oil - the distillate fuel commonly used for ECA compliance
• Specific fuel oil consumption - the engine efficiency metric central to EEDI / EEXI
• Exhaust gas cleaning system - the scrubber technology used as a Regulation 14 equivalent
• Selective catalytic reduction - the SCR after-treatment used for Tier III NOx compliance
• Marine diesel engine - the engine technology subject to Regulation 13 NOx limits
• LNG fuel system - the gas-handling system on dual-fuel ships
• Port state control - the enforcement mechanism for Annex VI in foreign ports
• Classification society - the Recognised Organisations conducting Annex VI surveys
• Flag state and flag of convenience - the flag-state responsibility for Annex VI
• COLREGs Convention - the parallel IMO instrument addressing collision avoidance
• Regulation 5 calculator - Annex VI survey cycle
• Regulation 6 calculator - IAPP certificate issue and endorsement
• Regulation 7 calculator - certificate duration and validity
• Regulation 10 calculator - port state control on operational requirements
• Regulation 12 calculator - ozone-depleting substances
• Regulation 13 calculator - NOx engine certification
• Regulation 14 calculator - sulphur cap and ECA limits
• Regulation 15 calculator - VOC management on tankers
• Regulation 16 calculator - shipboard incineration
• Regulation 18 calculator - bunker delivery note and fuel quality
• Regulation 21 calculator - EEDI required value
• Regulation 22 calculator - SEEMP Part I
• Regulation 22A calculator - IMO DCS data collection plan
• Regulation 23 calculator - transfer of efficiency technology
• Regulation 25 calculator - EEXI
• Regulation 26 calculator - SEEMP Part III revised
• Regulation 27 calculator - IMO DCS data submission
• Regulation 28 calculator - CII rating
• Tier II NOx limit calculator - rated-speed-dependent Tier II NOx
• Tier III NOx limit calculator - rated-speed-dependent Tier III NOx
• SOx from fuel sulphur calculator - SOx mass-emission rate from sulphur content
• PM10 / PM2.5 calculator - particulate matter emission estimate
• Black carbon calculator - IMO-recommended Black Carbon Reference Method
• Methane slip calculator - LNG dual-fuel methane-slip mass rate
• Methane slip CO₂-equivalent calculator - GWP100 / GWP20 conversion
• SOx scrubber NaOH dosing calculator - open-loop scrubber chemistry
• EGR rate Tier III calculator - exhaust gas recirculation rate
• Thermal NOx Zeldovich calculator - first-principles NOx formation
• Filter smoke number to BC calculator - FSN-to-BC conversion
• VOC management calculator - Regulation 15 compliance
• Crude tanker VOC calculator - loading-displacement vapour estimate
• Shipboard incinerator calculator - throughput-rate verification
• FONAR calculator - fuel oil non-availability report
• Bunker quality dispute calculator - BDN sample-test variance
• Fuel oil sampling calculator - sampling and chain-of-custody
• BDN reconciliation calculator - on-board fuel reconciliation
• Norway NOx Fund calculator - national NOx levy
• ESI score calculator - Environmental Ship Index
• IMO DCS report calculator - annual fuel report
• EU MRV emissions calculator - parallel European reporting
• MARPOL EU ETS cost calculator - EU ETS surrender cost
• MARPOL FuelEU penalty calculator - FuelEU non-compliance penalty
• SFOC-to-CII converter - engine SFOC to ship CII rating
• LNG WtW calculator - LNG well-to-wake intensity
• ShipCalculators.com calculator catalogue - full listing of MARPOL Annex VI and related maritime calculators

References

1. IMO. MARPOL Consolidated Edition 2022, including Protocol of 1997 and all subsequent amendments. IMO, London, 2022. Sales No. IB520E.
2. IMO MEPC. Resolution MEPC.176(58) - Amendments to MARPOL Annex VI (revised Annex VI). IMO, 10 October 2008.
3. IMO MEPC. Resolution MEPC.203(62) - Amendments to MARPOL Annex VI (Chapter 4 on energy efficiency). IMO, 15 July 2011.
4. IMO MEPC. Resolution MEPC.245(66) - Guidelines on the Method of Calculation of the Attained Energy Efficiency Design Index (EEDI) for New Ships. IMO, 4 April 2014.
5. IMO MEPC. Resolution MEPC.231(65) - Guidelines for Calculation of Reference Lines for Use with the Energy Efficiency Design Index (EEDI). IMO, 17 May 2013.
6. IMO MEPC. Resolution MEPC.282(70) - Amendments to MARPOL Annex VI (data collection system). IMO, 28 October 2016.
7. IMO MEPC. Resolution MEPC.328(76) - Amendments to MARPOL Annex VI (EEXI, CII, SEEMP Part III). IMO, 17 June 2021.
8. IMO MEPC. Resolution MEPC.336(76) - 2021 Guidelines on the Operational Carbon Intensity Indicators. IMO, 17 June 2021.
9. IMO MEPC. Resolution MEPC.339(76) - 2021 Guidelines on the Operational Carbon Intensity Rating of Ships. IMO, 17 June 2021.
10. IMO MEPC. Resolution MEPC.350(78) - Amendments to the 2021 Guidelines on Operational Carbon Intensity. IMO, 10 June 2022.
11. IMO MEPC. Resolution MEPC.364(79) - 2022 Guidelines on the Method of Calculation of the Attained EEXI. IMO, 16 December 2022.
12. IMO MEPC. Net-Zero Framework: Approval Document. MEPC 83, April 2025. 12a. IMO MEPC. Resolution MEPC.391(81) - 2024 Guidelines on Life Cycle GHG Intensity of Marine Fuels (2024 LCA Guidelines). IMO, 22 March 2024. 12b. IMO. Extraordinary MEPC session (MEPC/ES.2) adjourns Net-Zero Framework adoption. IMO Press Briefing, 17 October 2025.
13. IMO. Fourth IMO GHG Study 2020. IMO, London, 2020.
14. Comer, B. et al. Black Carbon Emissions and Fuel Use in Global Shipping, 2015. International Council on Clean Transportation, Washington, 2017.
15. CE Delft. Compliance with the 0.50% Sulphur Limit in International Shipping. Report for the European Commission, Delft, 2021.

Further reading

• IMO. MARPOL Annex VI: A Short Guide. IMO Publishing, London, 2014.
• Lloyd’s Register. Implementing the Energy Efficiency Design Index. Lloyd’s Register Marine, London, 2018.
• DNV. Maritime Forecast to 2050. DNV, Oslo, annual editions 2017 to 2025.
• IMO MEPC. NOx Technical Code 2008 (Resolution MEPC.177(58), as amended). IMO Publishing, London.
• Christiansen, P. and Bekiari-Skopa, A. The Net-Zero Framework: Architecture and Open Questions. WMU Journal of Maritime Affairs, 2025.