International Convention for the Prevention of Pollution from Ships

The International Convention for the Prevention of Pollution from Ships — universally abbreviated MARPOL — is the principal international instrument regulating pollution from vessels. It was adopted under the auspices of the International Maritime Organization (IMO) on 2 November 1973 and subsequently modified by the Protocol of 1978, which was adopted in response to a spate of tanker accidents in 1976–77. The combined instrument is referred to as MARPOL 73/78 and entered into force on 2 October 1983. A further 1997 Protocol added rules on air pollution.

MARPOL is structured around six technical Annexes, each addressing a distinct pollution source:

• Annex I — oil (in force 1983)
• Annex II — noxious liquid substances carried in bulk (1987)
• Annex III — harmful substances carried in packaged form
• Annex IV — sewage from ships
• Annex V — garbage from ships
• Annex VI — air pollution, including SOx, NOx, and (via later amendments) greenhouse gas measures such as the EEDI and the 0.50% global sulphur cap that took effect 1 January 2020

The Convention applies to ships flying the flag of a State Party and to ships operating under the authority of a Party. Enforcement is shared between flag States, which certify compliance and issue documents such as the IOPP Certificate, and port States, which inspect foreign vessels under regional memoranda like the Paris MoU. Special Areas and Emission Control Areas (ECAs) — for example the Baltic Sea, North Sea, and North American ECA — impose stricter discharge or emission limits.

MARPOL works alongside UNCLOS Article 211, which obliges States to adopt vessel-source pollution rules, and is administered by the IMO's Marine Environment Protection Committee (MEPC), which regularly adopts amendments under the tacit acceptance procedure.