Insights · Compliance · MARPOL
MARPOL is the single most important treaty standing between the world fleet and a polluted ocean. It governs what a ship may and may not put into the sea or the air — oil, chemicals, sewage, rubbish and exhaust gases — and it is enforced on every vessel that calls at a port that has ratified it.
Almost every environmental rule a merchant ship has to obey at sea traces back to one document. MARPOL — short for the International Convention for the Prevention of Pollution from Ships — is the main international convention covering prevention of pollution of the marine environment by ships from operational or accidental causes. Where the IMO number answers which ship you are looking at, MARPOL answers what that ship is allowed to discharge — and what it must do to prove it stayed within the limits.
The convention was adopted at the International Maritime Organization on 2 November 1973. A wave of tanker casualties in 1976 and 1977 exposed gaps in the original text before it had even entered into force, so the IMO bolted on the Protocol of 1978; the two instruments are read together as a single treaty known as MARPOL 73/78. It finally entered into force on 2 October 1983, when its first two Annexes took effect. A further 1997 Protocol later added a sixth Annex on air pollution.
MARPOL is not a single list of rules. The core articles are deliberately thin, and the substance sits in six technical Annexes, each one a self-contained code for a different category of pollutant. This modular design is what has let MARPOL keep up with the science: a new concern such as air emissions could be added as a whole new Annex without reopening the rest of the treaty.
| Annex | Subject | In force |
|---|---|---|
| I | Pollution by oil | 2 Oct 1983 |
| II | Noxious liquid substances in bulk (chemicals) | 1987 |
| III | Harmful substances carried in packaged form | 1992 |
| IV | Sewage from ships | 27 Sep 2003 |
| V | Garbage from ships | 31 Dec 1988 |
| VI | Air pollution from ships | 19 May 2005 |
Annexes I and II are mandatory for every party to the convention — you cannot ratify MARPOL and opt out of the oil and chemical rules. Annexes III to VI are technically optional, but they have been ratified so widely that, in practice, they bind the overwhelming majority of the world's gross tonnage. A modern ship trading internationally is built and operated to satisfy all six.
The original heart of MARPOL, Annex I, controls pollution by oil. It sets strict limits on how much oil a ship may discharge with its bilge or ballast water, requires oily-water separators to clean that water before it goes overboard, and mandates an Oil Record Book in which every relevant operation is logged. It also drives much of modern tanker construction: segregated ballast tanks and, after the major spills of the 1980s and 1990s, double-hull requirements that keep the cargo away from the outer skin of the ship.
Annex II governs noxious liquid substances carried in bulk — the chemical-tanker trade — categorising cargoes by the harm they would do and dictating how tank washings may be disposed of. Annex III extends the principle to harmful substances carried by sea in packaged form, setting rules on packing, marking and stowage. Annex IV deals with sewage, restricting untreated discharge near land. Annex V tackles garbage and is famous for one blanket prohibition: the disposal of plastics into the sea is banned outright, anywhere.
The newest Annex, added by the 1997 Protocol and in force since 19 May 2005, moved MARPOL from the water into the air. It caps sulphur oxides (SOx) and nitrogen oxides (NOx) in ships' exhaust, with stricter limits inside designated Emission Control Areas (ECAs) such as the North Sea and Baltic. The global sulphur limit it underpins is the rule the industry knows as IMO 2020.
Annex VI has since become the home of the IMO's energy-efficiency and decarbonisation work. It carries the EEDI, a design index for newbuildings; the EEXI, the equivalent benchmark applied to existing ships; and the CII, the operational carbon-intensity rating that grades a ship A to E each year on the emissions of its actual voyages. Together these three turn a clean-air Annex into the backbone of shipping's climate regime — explained further in our pieces on EEXI and EEDI and CII ratings.
The aim of the convention is to preserve the marine environment through the complete elimination of pollution by oil and other harmful substances and the minimisation of accidental discharge of such substances. International Convention for the Prevention of Pollution from Ships (MARPOL), IMO
A treaty is only as good as its enforcement, and MARPOL leans on two complementary checks. First, the ship's flag state certifies compliance — for oil, this is the International Oil Pollution Prevention (IOPP) certificate, with parallel certificates for the other Annexes. Second, when the ship enters a foreign port, Port State Control inspectors can board, examine those certificates and the record books, and detain a vessel that falls short. The regional regimes that coordinate this work, such as the Paris MoU, are how a coastal state holds foreign-flagged ships to the same standard as its own.
For anyone screening a fleet, the practical takeaway is that MARPOL compliance is a moving picture, not a single stamp. A ship's certificates, its ECA exposure and its CII grade all feed into how clean — and how trade-ready — it really is. You can look up any vessel's particulars and its broader compliance standing in the Marifest registry, and read the plain-English definitions of every term above in the maritime glossary.
How Marifest uses it
Marifest reads each ship through the lens of the convention that governs it, so the registry shows not just what a vessel is, but how clean it has to be. Every record links the hull to the Annexes that bind it and the regimes that police them.
Each ship's air-emissions standing — sulphur regime, NOx tier and the CII grade where available — sits in the vessel record, so Annex VI is visible at a glance, not buried in a certificate.
The live map shows where the stricter ECA limits apply, so you can see when a vessel is trading inside the North Sea, Baltic or other controlled waters.
MARPOL standing sits alongside sanctions screening in the compliance view, so the environmental and legal pictures of a hull are read off the same page.
Because every record is keyed to the IMO number, a ship's MARPOL history follows the hull through any rename or reflagging — the same fixed identity certificates rely on.