MARPOL Annex VI Reg 15: VOC emissions on tankers

Background: Annex VI 1997 + 2008 MEPC.176(58) + 2015 MEPC.255(67)

Air pollution from ships, and specifically the volatile organic compound (VOC) fraction of cargo and fuel emissions, was outside the scope of the original 1973 MARPOL Convention. The first international treatment came with the 1997 Protocol to MARPOL adopted at the International Conference of the Parties convened at IMO headquarters in London in September 1997, which appended Annex VI as a separate annex covering air pollution and ozone-depleting substances and entered into force on 19 May 2005 once the threshold of fifteen states representing at least 50% of world merchant gross tonnage was reached by Samoa’s accession on 18 May 2004.

The original 1997 text of Regulation 15 contained two short paragraphs: paragraph 15.1 obliged ports and terminals designated by their administration as VOC-regulated to provide a vapour-emission-control system; paragraph 15.2 obliged tankers calling at such ports and terminals to be fitted with a vapour-collection system meeting an IMO standard yet to be developed at adoption. The 1997 text addressed only crude oil carriers because crude oil is the cargo with by far the highest vapour-pressure and the largest commercial VOC emission load; product carriers carrying gasoline, naphtha and similar light products were left to the regional regimes of the EU and US EPA.

The 2008 revision of Annex VI under Resolution MEPC.176(58) of 10 October 2008 retained the structure of Regulation 15 but extended it materially. Three changes mattered. First, the IMO adopted in parallel Resolution MEPC.185(59) of 17 July 2009, which set out Guidelines for the development of a VOC Management Plan with a sample VOCMP template and operational checklist. Second, the revised Annex VI inserted a new paragraph 15.6 making the VOC Management Plan mandatory for crude oil carriers of 150 gross tonnes and above from 1 January 2010, an obligation that travels with the ship under flag-state law and is verified by port-state-control inspectors during the IAPP renewal survey. Third, the revised Annex VI created Appendix VII to list ports notified by their administration as VOC-regulated, replacing the earlier informal arrangement under which administrations notified the IMO Secretariat by ad-hoc circular.

A further amendment came under Resolution MEPC.255(67) of 17 October 2014, which clarified the procedure by which administrations notify ports and terminals to the IMO and harmonised the trigger conditions under which Reg 15.1 and 15.2 attach. The 2014 amendment also confirmed that VEC infrastructure provided under Reg 15.1 must be operationally available, not merely physically present, and that commercial unavailability (a loaded berth, a maintenance outage, an upstream pressure constraint) does not exempt a tanker from the Reg 15.6 VOCMP obligation.

The current state of the regulation, as of 2026, therefore comprises the 1997 base text as revised by MEPC.176(58) of 2008 and clarified by MEPC.255(67) of 2014, with the VOCMP guidelines in MEPC.185(59) of 2009 and a notified-port list in Appendix VII of more than 40 entries that grows by one to two entries per year as new terminals come into VEC service.

Reg 15.1 port + terminal VEC system requirement

Regulation 15.1 addresses the port-state side of the equation. It provides that any party to Annex VI that intends to have its ports or terminals considered VOC-regulated for the purposes of Regulation 15 shall notify the IMO Secretariat of its designation. The notification must specify the cargoes and tanker sizes to which the designation applies, the date of effect, and any later amendments. Once notified, the port or terminal is listed in Appendix VII to Annex VI and the obligation under 15.1 attaches.

The substantive 15.1 obligation is that the designating party must ensure that vapour emission control systems, approved by the administration and taking into account the safety standards in MEPC.185(59) and the wider SOLAS and MSC/Circ.585 framework, are provided in any ports and terminals so designated and are operated safely and in a manner that avoids undue delay to the ship. MSC/Circ.585, published in 1996 as the IMO’s Guidelines for Vapour Control Systems, predates the mandatory Annex VI framework and was the technical predecessor on which MEPC.185(59) built; the two instruments together define the ship-shore safety case. The phrase “operated safely” is not ornamental. VEC operations during crude loading bring together a flammable hydrocarbon vapour stream from the ship’s tanks, a shore reception system under positive or negative pressure, and an interconnect manifold that is the most failure-prone single component of the system. The 15.1 obligation is therefore a positive duty to design, install, commission and maintain the shore-side VEC such that the safety case for the combined ship-and-shore operation is at least as strong as the safety case for the same operation without VEC.

A further consequence of 15.1 is the obligation on the port state to ensure that the VEC system is commercially available on the same terms as any other terminal infrastructure, meaning that a tanker arriving at a designated berth and entitled to load is not denied loading because the VEC system is unavailable. Where the VEC system is unavailable for maintenance, regional and national regulators (notably the Norwegian Maritime Authority for the Norwegian crude terminals and the US Coast Guard plus regional EPA offices for US terminals) require advance notice through the agent and a documented maintenance window with an interim contingency.

The 15.1 obligation does not extend to imposing terminal VEC infrastructure on terminals not designated by the party. The Annex VI architecture is therefore opt-in for the port state and mandatory for the tanker once a port has opted in: a state can choose not to designate its terminals (in which case Reg 15.1 imposes no obligation and Reg 15.2 does not attach there), but once a state has designated a terminal, every visiting tanker must comply with Reg 15.2.

Reg 15.2 ship-side vapour-collection requirement

Regulation 15.2 is the flag-state and ship-side complement to 15.1. It provides that, where a tanker is bound for a port or terminal designated under 15.1, it shall be fitted with a vapour collection system approved by the administration, taking into account the safety standards developed by the IMO under MEPC.185(59) and consistent with MSC/Circ.585, and shall use such system during the loading of relevant cargoes.

Three points matter. First, the obligation attaches to the voyage, not to the ship at large. A crude tanker that never calls at a designated port is not obliged under 15.2 to fit a vapour-collection system, although in commercial practice every modern VLCC, suezmax and aframax built after 1997 has been fitted at construction because the Atlantic basin trade and the Norwegian and US terminals collectively make the absence of a VEC system commercially disabling. Second, the obligation runs through the flag administration, which approves the vapour-collection system by class survey and includes the VEC fitting in the International Air Pollution Prevention (IAPP) Certificate and its supplement. Third, the obligation is to fit and use, not merely to fit; the use obligation is enforced by the VOCMP procedural rules under 15.6 and by port-state-control deficiency codes for non-use during loading at a designated terminal.

The technical content of “vapour collection system” is set out in MEPC.185(59) and the parallel OCIMF Marine Vapour Emission Control Systems standard. The system comprises: (a) cargo-tank-top vapour piping routed to a dedicated vapour main; (b) a vapour manifold at the manifold platform with a standardised flange and coupling; (c) gas-detection and over-pressure / under-pressure protection in the vapour main; (d) the interface with the inert gas system which prevents oxygen ingress on the loaded side; and (e) the emergency shut-down (ESD) linkage with the shore VEC system. The class-society type-approval covers the entire chain from the cargo-tank top to the manifold flange.

The 15.2 obligation overlaps with the MARPOL Annex I inert gas system requirements on the safety side: a VEC system without an operating IGS is a flammable-mixture risk. The 15.2 vapour-collection system is therefore not an isolated retrofit; it is part of the integrated cargo-systems suite that includes the IGS, the cargo monitoring system, the cargo emergency shut-down, and the cargo control room.

Reg 15.6 VOC Management Plan (mandatory since 1 January 2010)

Regulation 15.6 is the operational complement to the engineering provisions of 15.1 and 15.2. It provides that every tanker carrying crude oil shall have on board and implement a VOC Management Plan approved by the administration. The plan must be specific to the ship, must take into account the guidelines developed by the IMO (MEPC.185(59)), must be written in the working language of the master and officers, and shall, at a minimum, provide written procedures for minimising VOC emissions during the loading, sea voyage, and discharge of cargo.

The mandatory date of 1 January 2010 for crude carriers of 150 gross tonnes and above was set in the 2008 revision and was deliberately chosen to give the existing fleet 14 months from MEPC.176(58) adoption (October 2008) to develop, approve and implement plans on board. The 150 GT threshold matches the threshold for the Oil Record Book under Annex I and ensures that the VOCMP travels with the same fleet that already keeps an ORB and a SOPEP.

The content of a VOCMP, as set out in MEPC.185(59), comprises eight elements. First, a description of the ship and the cargo systems including the inert gas system, the cargo tank arrangement, the vapour main, the manifold, and any VEC fitting. Second, a description of the VOC sources during normal operation: tank breathing on voyage, mass venting during loading, cargo-pump leakage, manifold disconnection. Third, the vapour pressure characteristics of the cargoes carried including TVP and RVP ranges and their temperature dependence. Fourth, operational procedures for loading at designated terminals (use of VEC), at non-designated terminals (closed-tank loading where compatible), and during the sea voyage (passive vent management, optional vapour-balance topping). Fifth, maintenance procedures for the vapour-main pressure and vacuum valves, gas-detection sensors, manifold seals, and ESD linkages. Sixth, training and familiarisation requirements for officers and ratings involved in cargo operations. Seventh, records including loading-rate logs, tank-pressure logs, gas-detection event logs, and the VOC emission estimate per cargo (an order-of-magnitude estimate based on cargo type, vapour pressure and VEC use). Eighth, review provisions: the plan must be reviewed when cargo systems change, when the ship changes flag, and at the IAPP renewal survey.

The VOCMP is flag-state-approved, not class-approved as a separate item, although the class society performs the underlying technical review and signs off on the engineering content. The approval is recorded in the IAPP supplement. MEPC.1/Circ.680 (2009) and its successor MEPC.1/Circ.719 (2013) provided supplementary technical guidance to flag administrations on the review criteria and approval process for VOCMPs submitted under Reg 15.6; administrations relying on these circulars apply a consistent standard across their fleets.

VOCMP scope: crude oil carriers of 150 GT and above

The scope of Reg 15.6 is intentionally narrow on the cargo side and broad on the ship side. Cargo side: only crude oil triggers the obligation. The VOCMP regime does not apply to product carriers loading gasoline, naphtha, jet fuel or other refined hydrocarbons, even though these cargoes have higher vapour pressures than many crudes and are subject to regional regimes (EU 94/63/EC, US EPA NSPS) that do require VEC at terminal level. The reason is historical: the 1997 negotiation focused on crude terminals because the volumes are larger by an order of magnitude (a single VLCC discharge replaces about 40 to 50 product-tanker discharges by parcel size) and the VOC mass per cargo is dominated by the crude trade.

Ship side: the obligation attaches to every crude oil carrier of 150 gross tonnes and above, with no upper bound, no flag exemption and no trade exemption. A 150 GT coastal crude shuttle from a domestic terminal must carry a VOCMP. A 320,000 dwt VLCC must carry a VOCMP. A combination carrier (oil-bulk-ore) carrying crude on a particular voyage must carry a VOCMP and must implement it for that voyage. The 150 GT lower bound exempts only the smallest service craft, river tankers and bunker barges that are not in international crude trade.

The “carrier” qualifier is important. A ship designated as a crude oil carrier in its Certificate of Fitness or Statement of Compliance must carry a VOCMP. A ship designated as a product carrier may carry crude only with flag-state approval and a temporary upgrade of the cargo-systems documentation; in that case the VOCMP must be added before the crude voyage commences. A ship that has never carried crude and never will (a chemical tanker, a clean-products tanker) need not carry a VOCMP.

Floating production storage and offloading units (FPSOs) and floating storage and offloading units (FSOs) operating on the Norwegian Continental Shelf, the UK North Sea, the Brazilian Campos and Santos basins, and West Africa carry crude in commercial quantities and are within the scope of Reg 15.6 if they are registered as ships under a flag. FPSOs registered as offshore installations under their host state’s petroleum-activity legislation are not formally within the IMO Annex VI scope but are covered by parallel offshore-petroleum-emissions regimes (notably the Norwegian VOCON 2008).

MEPC.185(59) VEC technical standard and the MSC/Circ.585 safety baseline

Resolution MEPC.185(59) of 17 July 2009 is the primary technical standard for vapour-emission-control systems referenced in Reg 15.1 and 15.2 and the source of the VOCMP guidelines under Reg 15.6. It was adopted at the fifty-ninth session of the MEPC and draws directly on MSC/Circ.585 (Guidelines for Vapour Control Systems, issued by the Maritime Safety Committee in 1996 and confirmed as the safety baseline in the revised Annex VI text). The resolution has three substantive parts plus an appendix.

The first part is the VEC system safety standard, derived from MSC/Circ.585 and the OCIMF Marine Vapour Emission Control Systems publication. It requires that the vapour-collection system shall include gas-detection equipment at the cargo-tank vapour main with a continuous monitoring capability and an alarm at not more than 30% of the lower explosive limit (LEL) of the carried hydrocarbon. The 30% LEL threshold is set well below the 100% LEL flammable-mixture threshold to provide a safety margin against measurement uncertainty and gas-stratification effects in the vapour main. MSC/Circ.585 established this threshold in the pre-mandatory era; MEPC.185(59) carried it into the mandatory framework without change.

The second part is the mechanical-protection standard. The vapour main must include high-vacuum and high-pressure protection to prevent (i) collapse of cargo-tank top under suction during VEC fault conditions and (ii) over-pressurisation of the cargo-tank top during shore-side flow restriction. The protection is typically a combination of pressure-vacuum valves at the cargo-tank tops, a pressure-vacuum breaker at the vapour main, and a rupture-disc safety device sized to handle the worst-case loading rate against a closed shore-side valve.

The third part is the manifold compatibility standard. The vapour manifold flange and coupling must conform to the OCIMF / ASTM marine vapour manifold standard which sets a single coupling geometry, flange face, bolt pattern and seal material such that any tanker fitted to the standard can mate with any shore-side vapour arm fitted to the same standard. The harmonisation is essential because tankers visit dozens of different VEC terminals across their commercial lives and any non-compatible coupling would force the tanker to refuse loading or the terminal to disable its VEC.

The fourth element of MEPC.185(59), which sits in the appendix, is the VOCMP template with section headings, recommended content and a worked example for a notional VLCC trading between West African crude terminals and the US Gulf coast.

The SOLAS Chapter II-2 framework for fire protection on tankers completes the mandatory safety envelope around VEC operations. SOLAS II-2 requires inert-gas systems on tankers above defined sizes and sets the operating-pressure regime that prevents air ingress to cargo tanks during loading. Without an operating IGS at positive pressure, a VEC connection creates the conditions for a flammable mixture in the vapour main, and both MSC/Circ.585 and MEPC.185(59) presuppose IGS compliance as the precondition for safe VEC operation.

IMO Annex VI Appendix VII designated ports (more than 40 as of 2026)

Annex VI Appendix VII is the IMO’s register of VOC-regulated ports and terminals notified by parties under Reg 15.1. The register is maintained by the IMO Secretariat and updated by MEPC circulars when a party notifies a new entry, an amendment or a withdrawal. As of 2026 the register contains more than 40 entries spanning Norway, the United States, Saudi Arabia, the United Arab Emirates, Mexico, Venezuela, Nigeria, the United Kingdom, Russia, China and Australia.

The pattern of designation reflects the regional politics of crude VOC. Northern Europe is the most heavily designated region because of the air-quality concerns of the Norwegian fjord communities around the crude-export terminals on the Norwegian west coast and the air-quality concerns of the German and Dutch port-cities around the North Sea trans-shipment terminals. The United States designated several major Gulf-coast and west-coast crude terminals in the 1990s under parallel EPA pressure. The Arabian Gulf designated the major crude-export terminals at Saudi and Emirati request once the EU regional pressure on imported crude began to attach. Latin America, Africa and Asia have a smaller number of designations, reflecting the lower priority of air-quality concerns relative to spill prevention and discharge control in those regions.

The Appendix VII listing is in principle the only authoritative source of which ports are VEC-regulated under Annex VI. In practice masters and operators rely on the OCIMF Vapour Emission Control Systems List which mirrors the IMO register and adds operational detail (terminal contact, VEC technology, manifold standard, current operational status). The OCIMF list is updated quarterly and is the working reference of charterers and tanker operators when fixing a voyage to confirm the VEC obligation.

Norway VEC-designated terminals: Sture, Mongstad, Stavanger

Norway is the founding country of the international VOC-regulation regime and the most heavily VEC-designated state in Annex VI Appendix VII. The Norwegian crude-export terminals on the west coast handle the bulk of North Sea production and have been the principal regional VOC source in Norwegian air-quality records since the 1980s.

The Sture terminal at the entrance to the Hjeltefjord, the export terminal for the Oseberg and Grane fields, was the first Norwegian terminal designated under the precursor regime in 1995 and was carried over into Annex VI Appendix VII at the 2010 entry into force. Sture is a vapour-recovery-unit (VRU) terminal: the displaced cargo vapour is compressed and condensed back to a liquid stream which is returned to the terminal storage tank, achieving a recovery efficiency of about 95% by mass.

The Mongstad terminal, north of Bergen, is the export terminal for the Troll, Gullfaks and Statfjord fields and is the largest crude terminal in Norway by throughput. Mongstad operates a hybrid VRU plus VCU configuration: the bulk of the displaced vapour is recovered through the VRU, with the residual fraction passed through the VCU thermal oxidiser as a polishing step. Mongstad’s combined VEC efficiency exceeds 99% by mass.

The Stavanger area terminals including the Kårstø gas-processing complex and the Risavika oil terminal complete the Norwegian designation footprint. These are smaller in throughput than Sture and Mongstad and operate VRU-only configurations with smaller VCU back-up.

The Norwegian regulatory framework is set by the Norwegian Environment Agency (Miljødirektoratet) under the Pollution Control Act and is implemented in operational detail by the Norwegian Petroleum Directorate. The combined effect of the Annex VI designation, the national pollution-control regime and the Norwegian VOCON 2008 bilateral with the United Kingdom on offshore loading is that essentially all crude exported from Norway is subject to VEC at the loading point.

US VEC-designated terminals: SF Bay, Galveston, Corpus Christi, Houston

The United States designated several major crude terminals under Annex VI Appendix VII in parallel with its domestic implementation of the EPA New Source Performance Standards for crude-oil loading. The principal designations are on the west coast and the Texas Gulf coast.

The San Francisco Bay terminals at Richmond, Martinez and Benicia, which serve the refineries of the Chevron Richmond, Phillips 66 Rodeo, Marathon Martinez and Valero Benicia complexes, were designated in the 1990s under Bay Area Air Quality Management District pressure. The Bay Area is in non-attainment for ozone under the US Clean Air Act and the local rules go beyond the Annex VI minimum: the Bay Area requires VEC efficiency above 95% and prohibits VCU-only configurations in favour of VRU plus polishing VCU.

The Galveston Bay terminals at Texas City, La Porte, and Baytown serve the refining complexes of Marathon Galveston Bay, ExxonMobil Baytown and Valero Texas City and were designated in the early 2000s. These are vapour-balancing-plus-VCU terminals: the bulk of the displaced vapour is balanced back to the shore tank in a closed loop and the residual fraction passes through the VCU.

The Corpus Christi terminals including the Ingleside, Magellan and EPIC export terminals, which became the largest US crude-export gateway after the 2015 lifting of the US crude-export ban, were designated in stages from 2018 to 2024 as new export berths came on line. The Corpus Christi terminals operate VRU configurations because the export trade favours liquid-product recovery over thermal destruction.

The Houston Ship Channel terminals at Houston, Pasadena and Texas City complete the US Gulf-coast footprint. These serve a mixed crude-import and product-export trade and operate combined VRU plus VCU configurations.

Saudi Arabia + UAE VEC-designated terminals

The Arabian Gulf is the second-largest crude-export region in Annex VI Appendix VII. Saudi Arabia and the UAE both designated their major crude-export terminals during the 2010s in response to EU regulatory pressure on imported crude and the parallel domestic priority on air-quality improvement in the major Gulf cities.

Saudi Arabia designated Ras Tanura on the Gulf coast (the historical principal crude-export terminal of Saudi Aramco), the King Fahd Industrial Port at Yanbu on the Red Sea coast (the western export terminal serving the East-West pipeline), and the Ju’aymah terminal north of Ras Tanura. The Saudi designations are consolidated under a single Aramco standard and use VRU-plus-VCU configurations with VRU primary.

The UAE designated the Fujairah crude-export terminal on the Gulf of Oman (a strategic east-of-Hormuz alternative to the Strait of Hormuz transit), the Jebel Ali terminal at Dubai (a refining and trans-shipment complex), and the Das Island offshore loading terminal in the Abu Dhabi offshore field. The UAE designations follow the Saudi VRU-plus-VCU pattern with local engineering by ADNOC and the Fujairah Oil Terminal operator.

The Saudi and Emirati designations together cover the bulk of Arabian Gulf crude export. Other Gulf states (Kuwait, Bahrain, Qatar, Iran, Iraq) had not designated their terminals as of 2026, although domestic discussion of designation has been live in Kuwait since 2020.

VEC technology 1: Vapour Recovery Unit (VRU)

A vapour recovery unit (VRU) is the technology of choice at terminals where the displaced cargo vapour has commercial value and the cost of compression and condensation is recoverable from the recovered liquid. The VRU is the highest-efficiency VEC technology and is the dominant choice in Norway and on the US west coast.

The VRU operates on a three-stage process. Stage 1: vapour separation. The displaced vapour from the ship’s vapour main enters the VRU at near-atmospheric pressure and passes through a knock-out drum that separates entrained liquid droplets, water and any free oil from the vapour stream. Stage 2: compression. The vapour passes to a multi-stage compressor (typically a screw or reciprocating compressor) which raises the pressure to 4 to 8 bar absolute, depending on the VRU design. Stage 3: condensation. The compressed vapour is cooled in a heat exchanger against ambient sea water or a refrigerant cycle, and the heavier hydrocarbon fractions condense to a liquid stream which is returned to the terminal storage tank as recovered product. The non-condensable fraction (mostly methane and ethane, and any inert gas carried over from the ship) is vented or sent to a polishing VCU.

The VRU recovery efficiency for a typical North Sea or West African crude is 90 to 97% by mass, with the residual loss in the non-condensable fraction. A polishing VCU brings the combined system efficiency above 99%. The recovered liquid product has commercial value: a 300,000 dwt VLCC loading at Sture displaces about 600 to 1,200 cubic metres of vapour during loading, of which the VRU recovers about 50 to 100 cubic metres of liquid hydrocarbon (light crude fraction equivalent to gasoline-range product), worth USD 30,000 to 80,000 at current prices.

The VRU capital cost for a single-berth installation is USD 15 to 35 million (2024 estimate) and the operational cost is dominated by the compressor electricity load (typically 1 to 3 MW) plus maintenance.

VEC technology 2: Vapour Combustion Unit (VCU)

A vapour combustion unit (VCU) is the alternative to a VRU at terminals where vapour recovery is not commercially attractive or where the displaced vapour quality (high non-condensable fraction, contamination) precludes recovery. The VCU destroys the VOC by combustion to CO2 and water vapour rather than recovering the hydrocarbon as liquid product.

The VCU operates on a single-stage thermal oxidation process. The displaced vapour enters the VCU through a flame arrester and detonation arrester, mixes with combustion air, and burns at 760 to 870 degrees Celsius (1,400 to 1,600 degrees Fahrenheit) in a refractory-lined combustion chamber. The combustion is supported by a pilot fuel (typically natural gas or LPG) which maintains the chamber temperature even when the vapour stream is too lean to support combustion alone. A modulating control adjusts the pilot fuel rate to maintain the design temperature as the vapour flow rate varies through the loading sequence.

The VCU destruction efficiency, when designed and operated to MEPC.185(59) and the OCIMF / ASTM standards, is at least 99.99%, meaning no more than 100 ppm of the input hydrocarbon escapes uncombusted at the stack. The combustion product is carbon dioxide and water vapour, which is climatically not benign (the CO2 is a greenhouse gas) but is air-quality benign at the local scale (the VOC and the associated ground-level ozone formation are eliminated).

The VCU capital cost is lower than the VRU at USD 5 to 12 million per single-berth installation, but the operational cost includes the pilot fuel burn (which is a continuous cost even when the terminal is not loading) and the CO2 emission (which has accounting consequences under the EU ETS Maritime extension and the IMO mid-term measures from 2027). The net commercial position therefore depends on the local electricity price, the local fuel price, and the local CO2 price.

The VCU is the default choice for terminals where the displaced vapour is too contaminated for VRU recovery, including some heavy-crude terminals where the vapour stream contains hydrogen sulphide or mercaptans that would foul the VRU compressor.

VEC technology 3: Vapour balancing (ship-shore closed loop)

Vapour balancing is the simplest and oldest VEC technology and is the default choice at terminals where the shore-side product is loaded from a fixed roof tank or a floating roof tank with a vapour space. The technique transfers the displaced cargo vapour from the ship’s tank back to the shore tank through a parallel vapour line, in a closed loop, such that the volume of vapour leaving the shore tank equals the volume of liquid leaving and the shore tank pressure remains constant.

The geometry is: the ship’s vapour manifold connects to the shore vapour arm; the shore vapour arm runs to the storage tank vapour space; the storage tank vapour pressure rises slightly above atmospheric; the tank breathing vent passes any minor excess pressure through a mechanical seal. The result is that the cargo vapour displaced from the ship goes into the shore tank and is reused on the next outload.

Vapour balancing has two limitations that determine its scope. First, it requires the shore tank to be a closed tank (a fixed roof, or a floating roof with a perimeter seal), not an open tank. Many older crude terminals at refinery sites have open or partially open tanks and cannot accommodate balancing without retrofit. Second, balancing does not destroy or recover the VOC; it merely defers the emission to the next outload. If the shore tank is not itself fed into a VRU or VCU when its inventory is drawn down to a refining process, the VOC escapes at that point. Balancing is therefore typically combined with a polishing VRU or VCU at the storage tank to handle the residual emission.

The balancing efficiency for the ship-to-shore segment is essentially 100% (no vapour escapes during the loading) but the system efficiency depends on the shore tank-vent management. Where the shore tank is connected to a VRU, the system efficiency is 90 to 97%; where the shore tank vents to atmosphere on the next outload, the system efficiency is essentially zero (the VOC is merely time-shifted).

The capital cost is the lowest of the three technologies at USD 0.5 to 2 million per berth, and the operational cost is essentially zero. Balancing is therefore the commercial default at terminals where the local regulatory regime permits it.

Gas detection: 30% LEL alarm threshold

The 30% LEL alarm threshold specified in MEPC.185(59) (and established in its predecessor MSC/Circ.585) is a safety threshold chosen to keep the operating concentration of the vapour main well below the lower explosive limit (LEL) of the cargo vapour.

The LEL of typical crude vapour is approximately 1.0 to 1.5% by volume in air, depending on the cargo and the temperature. A 30% LEL alarm therefore corresponds to a vapour-main hydrocarbon concentration of about 0.3 to 0.45% by volume, which is far below the 100% LEL threshold and provides a safety margin against measurement uncertainty, sensor drift and gas-stratification effects.

The gas-detection equipment is typically a catalytic-bead sensor for general hydrocarbon detection, supplemented by an infrared sensor for the methane and ethane fraction (which catalytic-bead sensors poorly detect because of poisoning and high-concentration response curve). The sensor is sited at the vapour main near the manifold and at the cargo-tank top in each tank, and is connected to the cargo control room and to the bridge through the integrated alarm and monitoring system.

The 30% LEL alarm triggers an automatic shut-down sequence: cargo loading stops, the shore-side ESD activates, the vapour-main isolation valve closes, and the cargo control room and bridge alarms sound. The shut-down sequence is integrated with the inert gas system to ensure that the post-shut-down tank atmosphere remains below the LEL (the IGS is the primary defence; the gas-detection alarm is the secondary defence and the ESD is the tertiary defence).

OCIMF / ASTM manifold coupling compatibility

The manifold-coupling compatibility standard is the unsung enabler of the entire VEC regime. The OCIMF / ASTM marine vapour manifold standard, referenced in MEPC.185(59), specifies the flange face geometry, the bolt circle and bolt count, the seal material and dimensions, and the dry-disconnect coupling (for terminals using rapid-connect arms rather than bolted flanges).

The harmonisation matters because tankers visit dozens of different VEC terminals across their commercial lives. A 320,000 dwt VLCC built in Korea and trading West Africa to US Gulf might call at Bonny (Nigeria), Sture (Norway), Houston (US Gulf), Singapore (lay-by), and Ras Tanura (Saudi Arabia) in a single annual cycle. Each of those terminals operates its own VEC arm, but every VEC arm conforms to the same manifold standard, so the same ship coupling mates with each arm without modification.

The standard also specifies the manifold platform layout at the ship: the vapour manifold is positioned at a defined distance and height from the cargo manifold to allow the VEC arm to clear the cargo arms, the platform handrails and the deck features. Modern tankers carry the vapour manifold on a dedicated extension of the manifold platform, with isolation valves and sample points at standardised positions.

Crude oil washing and VOC interplay

Crude oil washing (COW) under MARPOL Annex I Regulation 33 and SOLAS uses cargo itself to clean cargo-tank residues during discharge. The COW process and the Reg 15 VEC regime intersect in two places.

First, COW generates additional VOC during discharge: the jets of crude washing the tank surfaces produce a vapour-rich atmosphere in the tank even as the main cargo is being offloaded, and that VOC source does not attach to the designated-port trigger because it arises during discharge at the receiving terminal, not during loading. The VOCMP must account for COW as a separate VOC source and record the estimated COW-phase emission as part of the per-voyage record.

Second, the IGS interplay is tighter during COW than during loading. SOLAS requires that the cargo tanks be maintained in an inert condition (below 8% oxygen) throughout COW operations, and the VOC displaced by the COW jets mixes with the IGS atmosphere. The displacement to atmosphere is smaller per unit of COW volume than per unit of loading because the ullage space is shrinking, but it is not zero. A VOCMP that omits COW-phase VOC from its records will undercount the total voyage emission, which is a PSC deficiency item.

The distinction between loading-phase VEC (mandatory at designated ports under Reg 15.2) and discharge-phase COW-VOC (managed under the VOCMP but not subject to a VEC fitting requirement at the discharge terminal) is one of the more frequently misunderstood aspects of Reg 15 in PSC deficiency correspondence.

EU Directive 94/63/EC stage I terminal VOC controls

The EU Directive 94/63/EC of 20 December 1994 on the control of volatile organic compound emissions resulting from the storage of petrol and its distribution from terminals to service stations is the regional EU instrument that sits in parallel with Annex VI Reg 15. The Directive operates at three levels: stage I governs terminal-side emissions during product loading and storage, stage II governs service-station refuelling (vehicle vapour-recovery, not maritime), and the stage I.B intermediate level governs road-tanker and rail-tanker loading.

The maritime relevance is the stage I terminal-side regime, which requires every EU petrol-storage terminal to install a vapour-recovery unit with a recovery efficiency of at least 95% by mass and to operate it during all loading operations including ship loading. The Directive applies to petrol, defined as motor gasoline with vapour pressure above a defined threshold, and to associated naphtha and reformate streams; it does not apply to crude oil, heavy fuel oil, jet fuel, kerosene or marine gas oil.

The combined effect of EU 94/63/EC and Annex VI Reg 15 is that EU terminals are subject to both regimes for dual-trade ships (a product-tanker loading petrol falls under 94/63/EC; a crude-tanker loading at a designated terminal falls under Reg 15) and that EU member states have implemented both into a single national legal framework. The Directive was last amended by Directive 2009/126/EC which extended the regime to cover stage II vehicle refuelling but did not change the maritime stage I content.

US EPA NSPS 40 CFR 60 Subpart VVa marine vessel loading

The US EPA New Source Performance Standards under 40 CFR 60 Subpart VVa (and the parallel Subpart Kb for petroleum storage) is the US regional instrument that sits in parallel with Annex VI Reg 15 and the Clean Air Act regional rules.

Subpart VVa, in force since 1995 and amended several times, regulates marine vessel loading operations at US terminals handling petroleum liquids and chemical products. The substantive obligation is that any terminal loading more than 250,000 barrels per month of regulated product to marine vessels must install a vapour-emission-control system with a destruction or recovery efficiency of at least 95% by mass and must operate it during all loading operations.

Subpart VVa is the legal vehicle for the US Annex VI Appendix VII designations: a US terminal designated under Reg 15.1 is also subject to Subpart VVa (and to the parallel Bay Area, Houston-Galveston, or other regional rules). The two regimes overlap in scope and the US implementation routinely treats them as a single compliance package, with the more stringent requirement controlling.

The Bay Area Air Quality Management District Rule 8-44 and the Texas Commission on Environmental Quality Chapter 115 are the local rules that complete the US implementation framework.

Norwegian VOCON 2008 (Norway-UK FPSO + shuttle tanker)

The Norwegian-UK VOC Agreement of 2008, commonly known as VOCON 2008, is the bilateral instrument that addresses VOC emissions from offshore loading in the North Sea. The agreement entered into force on 1 January 2008 and binds the two states to a coordinated reduction of VOC from offshore crude loading from FPSOs and from shuttle tankers operating between FPSOs and shore terminals.

The substantive VOCON 2008 obligation is that the operating company of every offshore loading point on the Norwegian Continental Shelf and the UK Continental Shelf shall install and operate VOC-reduction equipment achieving a mass-emission reduction of at least 78% relative to the uncontrolled baseline. The VOCON benchmark is stricter than Annex VI Reg 15, which is qualitative and does not specify a percentage reduction.

The VOCON regime applies to shuttle tankers that lift crude from FPSOs and FSOs, requiring them to be fitted with VEC compatible with the FPSO offloading hose and the FPSO’s recovery system. Several major shuttle tanker operators (Knutsen NYK, Teekay, Viken Shipping) operate fleets that are 100% VOCON-compliant under flag-state Norway, UK and Singapore.

The VOCON regime does not apply to terminal-side loading at Sture, Mongstad or any other shore terminal; those are covered by the Norwegian domestic regime and Annex VI Reg 15. The combined effect is that Norwegian crude is subject to VEC at the FPSO offloading point, at the shuttle tanker, and at the shore terminal, achieving a near-100% VOC capture across the full export chain.

ISGOTT 6th edition 2020 chapter on VEC

The International Safety Guide for Oil Tankers and Terminals (ISGOTT) is the joint publication of OCIMF (Oil Companies International Marine Forum), ICS (International Chamber of Shipping) and IAPH (International Association of Ports and Harbors), first published in 1978 and now in its 6th edition of 2020. ISGOTT is the operational reference that sits between the IMO regulations and the ship and terminal operating procedures.

The ISGOTT 6th edition includes a dedicated chapter on vapour-emission-control systems (Chapter 11 in the 6th edition layout), which sets out the operational interface between the ship VEC and the shore VEC, the ship-shore safety checklist items specific to VEC operations, and the operational limits during VEC use. The chapter also includes the emergency procedures for VEC failures: detonation in the vapour main, fire at the manifold, gas alarm at 30% LEL, and shore-side power loss.

The ISGOTT chapter is not law, but it is incorporated by reference in the VOCMP under MEPC.185(59) and is the operational standard by which crew familiarity is assessed during PSC inspection. A crew that does not know the ISGOTT VEC chapter is unlikely to demonstrate VOCMP familiarity to a PSC inspector.

Relationship to MARPOL Annex I inert gas system

VEC and inert gas are inseparable. The inert gas system (IGS) under MARPOL Annex I Regulation 5 and the SOLAS Chapter II-2 fire-protection provisions maintains the cargo-tank atmosphere below the lower explosive limit during loading, voyage and discharge by displacing oxygen with combustion-product gas (CO2-rich) or inert gas from a generator. Without IGS, the displaced vapour during loading would mix with air and produce a flammable mixture in the vapour main; with IGS, the displaced vapour is inert-gas-rich and oxygen-poor, well below the LEL.

The VEC and IGS interact at three points. Point 1: cargo-tank top. The vapour leaving the cargo tank during loading is the inert gas plus crude vapour mixture displaced by the rising liquid level. The vapour main therefore carries a stream that is intrinsically below the LEL because the oxygen content is suppressed by the IGS. Point 2: vapour main. The vapour main is monitored at 30% LEL by the gas-detection equipment and protected against ingress of air from the shore side. Point 3: shore VEC. The shore VEC must accept an inert-gas-rich vapour stream, which has implications for the VRU compressor (the inert gas is non-condensable and must be vented) and for the VCU (the inert gas displaces combustion air and requires modulating control).

The integrated safety case is that IGS prevents the flammable mixture forming, VEC manages the emission of the non-flammable mixture, and the gas-detection plus ESD provide the secondary and tertiary defences.

Cargo VOC properties: TVP (ASTM D2879), RVP (ASTM D323)

The VOC emission rate during crude loading depends on the vapour pressure of the cargo, which is measured in two principal ways.

True vapour pressure (TVP) is the equilibrium vapour pressure of a hydrocarbon at a specified temperature, measured by ASTM D2879 or the equivalent IP 481 test. TVP is the engineering parameter for VEC sizing because it directly determines the partial pressure of hydrocarbon vapour in the cargo-tank atmosphere. TVP varies strongly with temperature: a typical North Sea crude has TVP of 0.3 to 0.5 bar at 15 degrees Celsius and 0.7 to 1.1 bar at 30 degrees Celsius, so the loading season and the cargo temperature matter materially.

Reid vapour pressure (RVP) is a standardised test under ASTM D323 in which a sample is held at 37.8 degrees Celsius (100 degrees Fahrenheit) in a defined air-to-liquid ratio and the resulting pressure is measured. RVP is a commercial specification parameter rather than an engineering parameter: it is used in cargo specifications and contracts to characterise the cargo’s evaporative loss tendency. The relationship between RVP and TVP is empirical and varies by crude type; the Bureau of Mines and the API have published correlation curves that allow conversion within about 10% accuracy.

The VOCMP requires the master to record the TVP and RVP for each cargo loaded, to estimate the VOC emission using the cargo properties and the loading conditions, and to document the VEC use including any cases where VEC was not available.

VLCC crude loading emissions without VEC: 0.5-1.5 g/kg

The uncontrolled VOC emission from a VLCC during crude loading is in the range 0.5 to 1.5 grammes of VOC per kilogramme of cargo loaded, varying with the crude type, the cargo temperature, the loading rate and the cargo-tank atmosphere management.

The lower bound of 0.5 g/kg corresponds to a heavy crude (Arabian Heavy, Maya, Bonny Heavy) loaded cool (10 to 15 degrees Celsius) at moderate rate with a well-managed inert gas system. The upper bound of 1.5 g/kg corresponds to a light crude (Brent, WTI, Bonny Light) loaded warm (25 to 30 degrees Celsius) at high rate with imperfect inert-gas management.

For a 300,000 dwt VLCC loading 270,000 tonnes of crude (the typical full-load parcel after deductions for ballast and slops), the uncontrolled VOC emission ranges 135 to 405 tonnes per loading. Across the world VLCC fleet of about 800 ships executing six to ten loadings per year, the uncontrolled fleet emission would be 600,000 to 3,000,000 tonnes per year of VOC. The actual fleet emission is far smaller because the majority of VLCC loadings now occur at VEC-equipped terminals.

With balancing: 0.1-0.3 g/kg; with VRU: 0.05-0.15 g/kg

The controlled emission with vapour balancing is 0.1 to 0.3 g/kg, a reduction of about 80 to 90% relative to the uncontrolled emission. The residual emission arises from the small fraction of vapour that is not captured by the balancing line (manifold disconnection losses, leakage at the vapour main, vent losses on the shore tank).

The controlled emission with a VRU, where the VRU captures the displaced vapour and condenses the heavier fractions, is 0.05 to 0.15 g/kg, a reduction of about 90 to 97% relative to uncontrolled. The VRU emission is dominated by the non-condensable fraction (methane, ethane, inert gas) that escapes the condenser and is vented or sent to a polishing VCU.

The controlled emission with a VCU only is in the 0.001 to 0.01 g/kg range because the VCU oxidises essentially all of the input hydrocarbon to CO2 and water; this is the lowest-emission configuration for VOC at the air-quality scale, although it does generate CO2 and is therefore not the lowest-greenhouse-gas configuration.

The VOCMP estimate of emission per cargo is built from these factors: the crude TVP, the cargo mass loaded, the cargo temperature and the VEC technology in use.

2024 MARPOL update: proposed product carrier expansion

The 2024 MARPOL review, currently under consideration at MEPC, proposes to extend the Reg 15 obligations to product carriers loading gasoline, naphtha, jet fuel and similar refined hydrocarbons at designated terminals. The proposal is supported by the EU member states, the United States and Norway, and is broadly opposed by the major flag states for product tankers (Marshall Islands, Liberia, Singapore) on cost-burden grounds.

The technical case is that product cargoes have higher vapour pressures than crude cargoes by a factor of two to ten, so the per-cargo VOC emission is materially larger per tonne for products than for crude. The volume offset is that product parcels are smaller, so the per-cargo absolute emission is similar. Across the world product fleet of about 4,000 ships executing 30 to 50 loadings per year, the uncontrolled fleet emission is comparable to the crude fleet uncontrolled emission and the marginal abatement value is similar.

The proposal was at the MEPC working group stage as of 2026 and is expected to be tabled for adoption at MEPC 84 in 2026 or MEPC 85 in 2027, with an entry-into-force date around 2030 if adopted.

Relationship to fuel oil tank vent under Reg 14

Reg 15 is principally about cargo VOC, but it also has a residual reach into fuel-oil tank vents on board the ship. The fuel oil tanks of any ship (cargo ship, tanker, container ship) are vented through dedicated vent risers to atmosphere, and the vent gas during fuel transfer at bunkering and during voyage temperature changes contains VOC.

The fuel-tank vent emissions are not directly regulated by Reg 15 (which addresses cargo only), but they are addressed indirectly by Reg 14 sulphur cap (the lower-sulphur fuels under IMO 2020 have lower VOC emissions because they are more refined) and by Reg 18 bunker delivery note (which records the fuel grade and provides an indirect VOC correlation).

Some flag states (notably Norway and the Netherlands) require domestic ferries and short-sea ships to fit fuel-tank-vent VEC under domestic legislation; this is not an Annex VI obligation but is consistent with the Annex VI direction of travel.

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

Every IACS class society has implemented Reg 15 type-approval and survey procedures for the vapour-collection system and the VEC system as a whole.

DNV publishes Class Notation VENT for vapour-collection systems and integrates the VOCMP review into the renewal survey of the IAPP supplement. Lloyd’s Register publishes parallel Class Notation ShipRight VEC procedures and includes the VEC review in the cargo-systems survey. ABS publishes the Marine Vapour Emission Control Systems Guide and surveys the VEC under the cargo-piping survey. Bureau Veritas, Nippon Kaiji Kyokai, RINA, Korean Register, China Classification Society, Russian Maritime Register of Shipping, and the Indian Register of Shipping each publish equivalent guidance and survey procedures. The IACS unified-requirement framework ensures that a tanker built to one society’s standard can transfer class to another without re-certification of the VEC system.

The class society also reviews the VOCMP at the IAPP renewal survey and documents any changes to the cargo-systems arrangement that affect the plan.

PSC inspection: VOCMP + crew familiarity + maintenance log

Port-state-control (PSC) inspectors verify Reg 15 compliance during routine and concentrated inspections. The principal items of inspection are: (i) presence of the VOCMP on board in the working language of the master; (ii) flag-state approval of the VOCMP; (iii) crew familiarity with the VOCMP, tested by interview of the chief officer and the cargo officer; (iv) the manifold-coupling type-approval documentation and the maintenance log of the gas-detection equipment, the pressure-vacuum valves, and the manifold seals; (v) records of VEC use at designated terminals on the recent voyage history.

A finding under Reg 15 is typically a deficiency rather than a detention item, except where the finding is of a non-functional gas-detection system or a non-existent VOCMP, in which case detention is the proportionate response. The Paris MoU and Tokyo MoU annual reports show low single-digit detention rates under Annex VI generally, with Reg 15 contributing a small fraction of the deficiency total.

Commercial implications: VRU capex/opex + crude price

The commercial calculus of VEC is asymmetric between the terminal operator and the tanker operator.

For the terminal operator, the VRU is a long-term capital investment with a recovery period of 10 to 25 years depending on throughput, the recovered-product price and the local regulatory premium. At a high-throughput VLCC terminal (Sture, Houston, Ras Tanura) the recovered-product value alone justifies the VRU capex; at a lower-throughput terminal the regulatory mandate is the deciding factor.

For the tanker operator, the VEC is a non-recoverable cost: the ship-side vapour-collection system has no liquid-product return, only a regulatory-compliance value. The capex is USD 0.5 to 2 million per ship at construction (much less if integrated at design) and the opex is dominated by the inspection and testing burden. Tanker operators have therefore lobbied for harmonisation of the manifold standard (achieved through OCIMF / ASTM) and against the extension of Reg 15 to product carriers (still under review).

VEC retrofit cost: USD 0.5-2 million per VLCC

The retrofit cost of a vapour-collection system on an existing VLCC is USD 0.5 to 2 million depending on the original cargo-systems design, the manifold layout and the dry-docking schedule.

The lower bound of USD 0.5 million applies to a VLCC built post-1997 with a pre-installed vapour main and manifold but without the gas-detection or ESD upgrade; the retrofit is then a series of bolt-on items completed during a normal dry-docking period. The upper bound of USD 2 million applies to a pre-1997 VLCC without any vapour main, where the retrofit requires routing new piping along the deck, modifying the manifold platform and integrating with the existing IGS and cargo-control systems. Most VLCCs in commercial service today were built post-2000 and were fitted with the vapour-collection system at construction, so the retrofit problem is mostly historical.

2030 outlook: product carrier expansion + decarbonisation linkage

The 2030 outlook for Reg 15 is shaped by two drivers. First, the product carrier expansion under MEPC review is expected to extend the regulation to gasoline, naphtha and jet-fuel cargoes and to cover an additional 4,000 ships in the world fleet. Second, the decarbonisation linkage under the IMO 2023 GHG Strategy and the 2027 mid-term measures connects VOC emission control with the broader greenhouse-gas regime, because the methane and ethane fraction of cargo VOC is a non-trivial methane source and methane is a potent greenhouse gas.

The combined effect is that Reg 15 is likely to expand both in cargo scope (crude plus products) and in pollutant scope (VOC plus methane) over the 2025-2035 horizon, with parallel changes to the VOCMP template to incorporate methane-specific procedures and to the VEC standard to incorporate methane-specific destruction or recovery requirements.

When a port regulates VOC: the emission triggers

Reg 15.1 and 15.2 attach the moment a tanker is bound for a terminal a party has notified to the IMO under Appendix VII. The quantity that the regulation exists to suppress is the VOC emission per loading, and the working estimate every VOCMP carries is the displacement product of cargo mass, an uncontrolled emission factor, and the VEC capture term:

Here $E_{\text{VOC}}$ is the total VOC emission for the loading (kg), $m_{\text{cargo}}$ is the cargo mass loaded (kg), $\varepsilon_{\text{cargo}}$ is the uncontrolled emission factor (g VOC / kg cargo), and $\eta_{\text{VEC}}$ is the VEC capture efficiency (0 to 1). The uncontrolled factor for crude sits in the band $\varepsilon_{\text{VOC, no VEC}} \in [0.5, 1.5]$ g/kg for a VLCC. Vapour balancing pulls it to $\varepsilon_{\text{VOC, balancing}} \in [0.1, 0.3]$ g/kg and a VRU to $\varepsilon_{\text{VOC, VRU}} \in [0.05, 0.15]$ g/kg. The capture terms behind those numbers are $\eta_{\text{VRU}} \approx 90$ to $97\%$ and $\eta_{\text{VCU}} \geq 99.99\%$ for a thermal oxidiser built and run to MEPC.185(59). Gas detection in the vapour main alarms at no more than 30% of the lower explosive limit, so the safety constraint that bounds the whole operation is $\text{LEL alarm} \leq 30\%$.

The physical origin of $\varepsilon_{\text{cargo}}$ is the gas-displacement law during loading. Each unit of liquid cargo entering the tank displaces an equal volume of the inert-gas-plus-vapour atmosphere above it. The hydrocarbon partial pressure in that atmosphere is approximately the true vapour pressure (TVP) of the cargo at the cargo-tank-top temperature, scaled down by the IGS dilution factor of roughly 0.7 to 0.9. The displaced vapour mass follows from the ideal-gas density of that hydrocarbon fraction:

where $V_{\text{cargo}}$ is the loaded volume, $p_{\text{TVP}}$ is the true vapour pressure (Pa), $M_{\text{hydrocarbon}}$ is the molecular weight of the vapour-phase hydrocarbon (kg/mol), $R$ is 8.314 J/mol/K, and $T$ is the cargo-tank-top temperature (K). For a North Sea crude at 20 degrees Celsius with TVP of 0.5 bar, the displaced vapour density is about 1.5 kg/m³. A VLCC loading 270,000 tonnes (300,000 dwt, 312,500 m³ displaced) then sheds about 470 tonnes uncontrolled, or 1.7 g/kg, at the upper end of the literature range. Apply a VRU at 95% efficiency with a polishing VCU at 99.99% and the combined capture is 99.7%, so the residual drops to about 1.4 tonnes per loading, 5 grammes per tonne of cargo, 0.005 g/kg.

The VOC Management Plan: assumptions baked into the estimate

The VOCMP emission estimate is a deliberate simplification, and a competent cargo officer treats its four assumptions as the boundary of its accuracy. It assumes a well-mixed cargo-tank atmosphere at uniform temperature and TVP. The real atmosphere stratifies, with the warmest, most vapour-rich layer at the tank top, so the estimate understates the peak rate during early loading (warm vapour leaves first) and overstates the late rate.

It assumes a single dominant vapour-phase hydrocarbon, typically a C5 to C7 fraction with $M_{\text{hydrocarbon}}$ between 70 and 100 g/mol. The real vapour spans C1 to C10, so the chosen molecular weight drives the accuracy. It assumes the IGS is operating and the atmosphere stays below the LEL throughout. On an IGS failure the atmosphere turns flammable, loading is suspended, and the estimate no longer applies because the operation is not lawful. It assumes the VEC runs at design efficiency, but the realised figure tracks the loading rate, the back-pressure, the ambient temperature and the maintenance status, and it usually sits slightly below the design value.

The plan turns those assumptions into the eight-element record set out earlier: the master logs the cargo TVP and RVP, estimates the per-cargo VOC mass from the cargo properties and loading conditions, and documents VEC use including any window where VEC was unavailable. The estimate is order-of-magnitude by design; its value is the trend across loadings, not a single tonne-precise figure.

Worked example: Bonny Light at Sture

Take a 300,000 dwt VLCC loading 270,000 tonnes of Bonny Light crude at the Sture terminal at a cargo-tank-top temperature of 20 degrees Celsius. The TVP at 20 degrees is about 0.55 bar. The displaced vapour volume at 1.05 bar absolute, slightly above atmospheric from the IGS over-pressure, is 312,500 / 1.05 = 297,600 m³, and the displaced vapour mass is about 460 tonnes uncontrolled. That is 1.7 g/kg of cargo, near the top of the literature range.

The Sture VRU runs at 95% capture with a polishing VCU at 99.99%, a combined 99.7%, so the residual emission is 1.4 tonnes for the loading. The VOCMP record entry reads: cargo mass 270,000 tonnes; cargo TVP 0.55 bar at 20 degrees Celsius; VEC technology VRU plus VCU; estimated VOC emission 1.4 tonnes; VEC use confirmed by terminal log. That single line is what a PSC inspector cross-checks against the gas-detection log and the terminal’s own record.

Compliance reference table

Limitations

This article presents Reg 15 and the supporting technical framework as reference material for cargo officers, port-state-control inspectors, chartering professionals and regulatory researchers. Five limits on the analysis should be understood.

Scope: The article covers Reg 15 as it stands in 2026 under MEPC.176(58) and MEPC.255(67). The proposed product-carrier extension is described as a proposal, not as adopted text. If MEPC 84 or MEPC 85 adopts the extension, the scope sections above will need updating.

Emission factors: The 0.5 to 1.5 g/kg uncontrolled emission range and the VEC-controlled ranges are derived from published literature and industry benchmarks as of 2024 to 2026. The actual per-ship figures vary with cargo, temperature and VEC maintenance state. The VOCMP estimate is order-of-magnitude, not regulatory-precision.

Port list: Annex VI Appendix VII is updated by MEPC circular continuously; the count of “more than 40 entries” is the 2026 figure. Operators must check the current IMO register or the OCIMF VEC list, not this article, to confirm current designations.

VEC efficiency: The VRU, VCU and balancing efficiency figures are typical-case ranges. A given terminal may operate above or below the stated range depending on equipment age, maintenance status and operational practices.

Regional law: The article describes EU 94/63/EC, US 40 CFR 60 Subpart VVa and Norwegian VOCON 2008 at summary level. Compliance in each jurisdiction requires checking the current national implementation, not the summary above.

See also

• MARPOL Annex VI: parent annex covering air pollution and ozone-depleting substances
• MARPOL Convention: top-level pollution-prevention treaty
• MARPOL Annex VI Regulation 12: ozone-depleting substances: companion air-pollution regulation
• MARPOL Annex VI Regulation 13: NOx Tier I, II, III: companion engine-NOx regulation
• MARPOL Annex VI Regulation 14: SOx + PM sulphur cap and SECA limits: companion fuel-sulphur regulation
• MARPOL Annex VI Regulation 16: shipboard incineration: companion shipboard waste regulation
• MARPOL Annex VI Regulation 17: reception facilities: port-side reception infrastructure regulation
• MARPOL Annex VI Regulation 18: Bunker Delivery Note: documentary verification framework
• MARPOL Annex I oil-pollution prevention: the parallel oil annex
• MARPOL Annex I Regulation 15 discharge control: the parallel oily-water discharge regime
• MARPOL Annex I Regulation 33: crude oil washing: COW interaction with VOC management
• Per-fuel WTW: VLSFO and MGO: the well-to-wake fuel emission breakdown
• IMO 2020 sulphur cap: the 0.50% global cap event
• Calculator catalogue

References

The canonical sources for this article comprise the IMO Air Pollution and Annex VI portal which sets out the structure of Chapter 3 of Annex VI, Resolution MEPC.176(58) of 10 October 2008 which adopted the revised Annex VI carrying Regulation 15 forward, Resolution MEPC.185(59) of 17 July 2009 which set out the Guidelines for the development of a VOC Management Plan including the sample VOCMP template (and which incorporates the safety baseline from MSC/Circ.585 of 1996), Resolution MEPC.255(67) of 17 October 2014 which clarified the notification procedure for VOC-regulated ports under Appendix VII, MEPC.1/Circ.680 (2009) and MEPC.1/Circ.719 (2013) which provided flag-administration guidance on VOCMP approval criteria, EU Directive 94/63/EC of 20 December 1994 on the control of volatile organic compound emissions resulting from the storage of petrol and its distribution from terminals to service stations as amended by Directive 2009/126/EC, the US EPA NSPS 40 CFR 60 Subpart VVa marine vessel loading provisions in force since 1995, the OCIMF / ICS / IAPH ISGOTT 6th edition 2020 International Safety Guide for Oil Tankers and Terminals with its dedicated chapter on vapour-emission-control systems, the Norwegian VOCON 2008 bilateral agreement between Norway and the United Kingdom on offshore VOC reductions on the North Sea continental shelves, the DNV and Lloyd’s Register Annex VI implementation guidance covering type-approval and survey of vapour-collection systems, the Paris Memorandum of Understanding port-state-control inspection library and Annex VI deficiency codes, and the ASTM D2879 test method for vapour pressure-temperature relationship and the parallel ASTM D323 Reid vapour pressure test method. Full citation links appear in the frontmatter.

Related calculators

• VOC Management - MARPOL VI Reg 15 Check
• MARPOL Annex VI/15 - VOC emissions
• MARPOL Annex V/9 - Placards garbage management plan
• Tanker Op - VOC management plan
• MARPOL Annex VI/14 - Sulphur emissions
• MARPOL Annex VI/13 - NOx emissions
• MARPOL Annex II/14 - Shipboard marine pollution plan NLS
• MARPOL Annex I/37 - Shipboard Oil Pollution Emergency Plan