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MARPOL regulations set the global standard for preventing pollution from ships, and every seafarer operating in international waters must understand them. Short for the International Convention for the Prevention of Pollution from Ships, MARPOL was adopted by the IMO in 1973 and amended by a Protocol in 1978 — hence the combined reference MARPOL 73/78. It covers everything from oil and chemicals to garbage, sewage, and air emissions.

Additionally, compliance is not optional. Port State Control officers inspect vessels against MARPOL requirements at every major port worldwide. Violations can result in detention, substantial fines, and reputational damage to the vessel, its operator, and its crew. This guide gives you the essentials for each Annex and what they mean in daily shipboard life.

What MARPOL Covers: The Six Annexes

MARPOL is structured around six Annexes, each addressing a different category of ship-generated pollution. Annexes I, II, and V are mandatory for all signatories; Annexes III, IV, and VI are optional but have been ratified by most major flag states.

• Annex I — Prevention of pollution by oil
• Annex II — Control of pollution by noxious liquid substances in bulk (chemicals)
• Annex III — Prevention of pollution by harmful substances in packaged form
• Annex IV — Prevention of pollution by sewage from ships
• Annex V — Prevention of pollution by garbage from ships
• Annex VI — Prevention of air pollution from ships (SOx, NOx, CO2)

Annex I: Oil Pollution Prevention

Furthermore, annex I is the cornerstone of MARPOL. It governs the discharge of oily water from machinery spaces, cargo residues from tankers, and the carriage of oil in fuel tanks. The key threshold is that oily water discharges from engine room bilges must not exceed 15 parts per million (ppm) and must only occur outside special areas, with an approved oily water separator in operation.

Every vessel subject to Annex I must carry an Oil Record Book (ORB). All oil transfers, bilge operations, and overboard discharges must be recorded. Entries must be signed by the officer in charge and the Master. Falsifying ORB entries is a criminal offence under most flag state laws and a common target of PSC inspections.

However, tankers additionally require an International Oil Pollution Prevention (IOPP) Certificate, a Shipboard Oil Pollution Emergency Plan (SOPEP), and Crude Oil Washing (COW) procedures where applicable.

Annex II: Noxious Liquid Substances (Chemicals)

Annex II applies to chemical tankers carrying noxious liquid substances (NLS) in bulk. Substances are categorised into four groups (X, Y, Z, and OS) based on hazard level. Category X substances present the greatest risk — their discharge into the sea is prohibited entirely. Categories Y and Z are subject to quantity and location restrictions.

In addition, chemical tankers must hold a Certificate of Fitness and carry a Cargo Record Book (CRB). Pre-washing procedures before tank cleaning are mandatory for many Category X and Y cargoes. Officers on chemical tankers require additional STCW V/1-1 or V/1-2 training certificates depending on the cargo type.

Annex V: Garbage Management

Annex V prohibits the disposal of plastics into the sea anywhere in the world — a zero-tolerance rule with no distance or location exceptions. Food waste, cargo residues, and other garbage have varying discharge restrictions depending on distance from the nearest land and whether the vessel is in a Special Area.

Importantly, all vessels over 100 GT and those certified to carry more than 15 persons must carry a Garbage Management Plan and maintain a Garbage Record Book. The plan must designate a responsible officer and describe procedures for minimising, collecting, storing, processing, and discharging garbage.

“MARPOL compliance comes down to documentation and crew awareness,” notes a Chief Officer with 18 years on bulk carriers and container ships. “The Oil Record Book and Garbage Record Book must be accurate, up to date, and available for inspection at any time. Officers who treat these as formalities rather than genuine records create serious risk for themselves and their company.”

Annex VI: Air Pollution — SOx, NOx, and the Energy Efficiency Rules

Notably, annex VI is increasingly important as the IMO accelerates decarbonisation. It sets global sulphur limits for marine fuel (0.50% m/m globally since 2020, and 0.10% in Emission Control Areas), NOx emission standards for diesel engines by tier, and energy efficiency requirements under the EEDI/EEXI/CII framework.

Emission Control Areas (ECAs) currently cover the Baltic Sea, North Sea, North American coastal waters, and the US Caribbean Sea area. Vessels in these zones must burn fuel with sulphur content no higher than 0.10% — or use an approved exhaust gas cleaning system (scrubber). Masters and Chief Engineers must ensure the bunker delivery note (BDN) and fuel samples are retained on board and match the logged fuel changeover records.

In practice, from 2023, the Carbon Intensity Indicator (CII) rating applies to ships over 5,000 GT. Ships receive an annual A–E rating based on fuel consumption relative to transport work. A poor CII rating can trigger enhanced PSC scrutiny, so Chief Engineers and Masters should understand their vessel’s CII performance and what operational changes can improve it.

Special Areas Under MARPOL

Special Areas are sea zones where stricter discharge rules apply because of their particular oceanographic or ecological sensitivity. The Baltic Sea, Mediterranean Sea, Black Sea, Red Sea, Gulfs Area, Gulf of Aden, and Antarctic Area all have Special Area status under one or more Annexes. In these zones, even discharges that would be permitted in open ocean are prohibited or more tightly regulated.

Before entering a Special Area, the officer on watch and the Chief Officer or Chief Engineer should confirm that the vessel is operating within the applicable Annex restrictions. Entering a Special Area without a functional oily water separator, for instance, can constitute a MARPOL violation even if no discharge occurred.

Key MARPOL Documents Every Officer Must Know

• Oil Record Book (ORB) — Parts I (machinery spaces) and II (cargo/ballast operations for tankers)
• Garbage Record Book (GRB) — All vessels ≥100 GT or certified for 15+ persons
• Cargo Record Book (CRB) — Chemical tankers under Annex II
• IOPP Certificate — International Oil Pollution Prevention Certificate (tankers and relevant ships)
• SOPEP — Shipboard Oil Pollution Emergency Plan
• Garbage Management Plan — Required procedure document on board
• Bunker Delivery Notes — Retained for 3 years; sulphur content must be verified
• International Energy Efficiency Certificate (IEEC) — For ships ≥400 GT

Tips for MARPOL Compliance on Board

• Make record book entries in real time — never reconstruct them after the fact
• Know which Annexes apply to your vessel type and trade area
• Brief crew on plastic waste rules and Special Area restrictions before entering sensitive zones
• Test and maintain the oily water separator regularly; ensure the 15ppm alarm is operational
• Keep the Chief Engineer informed of any planned bilge transfers before execution
• Verify sulphur content of bunkers against the BDN immediately on delivery
• Report any accidental pollution to the Master immediately — early reporting mitigates penalties

MARPOL compliance is ultimately a shared responsibility across the entire crew. The Master holds ultimate accountability, but every officer and rating plays a role in keeping records accurate and operations within the rules. Internal links for further reading: see our guide to Port State Control Inspections and the STCW Certification Guide for related compliance requirements.

Frequently Asked Questions

What is MARPOL and which ships does it apply to?
MARPOL (International Convention for the Prevention of Pollution from Ships) applies to virtually all vessels operating in international waters, including merchant ships, tankers, bulk carriers, passenger ships, and offshore vessels. Flag state implementation means it also applies in many national waters.

How many Annexes does MARPOL have?
MARPOL has six Annexes. Annexes I (oil), II (chemicals), and V (garbage) are mandatory for all signatory states. Annexes III (packaged substances), IV (sewage), and VI (air pollution) are optional but widely ratified.

What is the global sulphur limit under MARPOL Annex VI?
Since 1 January 2020, the global sulphur limit for marine fuels is 0.50% m/m. In Emission Control Areas (ECAs), the limit is stricter at 0.10% m/m. Ships can also comply by using approved exhaust gas cleaning systems (scrubbers).

What happens if a ship violates MARPOL regulations?
Violations can result in port state detention, substantial fines under national law, flag state penalties, and criminal prosecution of the responsible officers in serious cases. Falsification of record books is treated particularly harshly and has led to prison sentences for senior officers.

Do MARPOL rules apply in port as well as at sea?
Yes. MARPOL applies whenever a vessel is within the jurisdiction of a signatory state, which includes ports and internal waters. In fact, port state control inspections are the primary enforcement mechanism for MARPOL compliance.

Conclusion

Understanding MARPOL regulations is a non-negotiable part of serving as an officer on any internationally trading vessel. Whether you work in deck, engine, or catering departments, knowing the rules that apply to your vessel type and trade area protects you, your crew, and the marine environment.

Stay current with IMO amendments — the regulations continue to evolve, especially around air emissions and carbon intensity. For officers looking to advance into senior roles where MARPOL compliance responsibility increases, browse maritime career opportunities at Seaplify.

For official maritime standards and further information, visit the International Maritime Organization (IMO).