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Tanker dumping oil from cargo tank in the 1970’s

Photo Credit: t3media

Until the mid-twentieth century, it was general practice for commercial ships to simply pump sludge and oily bilge-water into the sea.

These rules were strengthened following the wreck of the Torrey Canyon off the coast of England in 1967, through the creation of an international marine treaty on oil pollution known as MARPOL.

MARPOL was designed to eliminate oil pollution in the seas.

MARPOL was written in 1973 and revised in 1978 by the International Maritime Organization, a United Nations group that supervises the safety and security of international shipping and works to prevent marine pollution by ships.

MARPOL has six sections, known as annexes, each addressing a different kind of pollution.


Oily water separators do not allow oil to be discharged at more than 15 ppm

Photo Credit: Common Good Productions

Annex I: Oil
Annex II: Noxious Liquid Substances carried in Bulk
Annex III: Harmful Substances carried in Packaged Form.
Annex IV: Sewage
Annex V: Garbage
Annex VI: Air Pollution

The first section, Annex I, deals with oil pollution.

In addition to setting standards for oil tanker construction, this section establishes two key rules relating to commercial ships and oil:

1. All commercial ships must maintain an accurate oil record book to document the movement and fate of all oil brought on board.

2. Oily wastewater on ships must be processed by a properly working oily water separator equipped with a functioning oil content monitor. Discharge through the oily water separator cannot contain more than fifteen parts per million of oil.

ALERT! Fifteen parts of oil per million of water is an invisible amount of oil in water. Any release of oily waste that produces a visible sheen is illegal.


According to MARPOL Annex I, Part C, Regulation 15, “Any discharge into the sea of oil or oily mixtures from ships of 400 gross tonnage and above shall be prohibited except when all the following conditions are satisfied:

1. The ship is proceeding en route;
2. The oily mixture is processed through an oil filtering equipment meeting the requirements of regulation 14 of this Annex;
3. The oil content of the effluent without dilution does not exceed 15 parts per million;
4. The oily mixture does not originate from cargo pump room bilges on oil tankers; and
5. The oily mixture, in case of oil tankers, is not mixed with oil cargo residues.”


One hundred and thirty-six countries, including the United States, have signed the MARPOL convention. This covers 98% of the world’s shipping tonnage, and every signatory is required to enact domestic laws to implement the treaty and enforce compliance.

In the United States, the legislation implementing MARPOL is known as the Act to Prevent Pollution from Ships.

Click here to see the laws relating to oil pollution in the United States.

When ships come to US ports they are subject to inspection by the United States Coast Guard. Coast Guard officers are there to make sure that all ships that enter US waters do so safely and comply with US and international laws.

Often, when crimes on a vessel are committed, concerned crewmembers, known as whistleblowers, will come forward with evidence of pollution. Because these men and women risk their livelihoods to help keep the seas clean, they are often eligible for up to half of the fines paid by polluting companies if a ship is successfully brought to justice.


1959 IMO assembly in London

Photo Credit: International Maritime Organization


Annex I specifies special areas that are subject to additional protection with respect to oil pollution. These areas are determined based on ecological or oceanographic importance and are provided with a higher level of protection than other areas of the sea.

Mediterranean Sea
Baltic Sea
Black Sea
Red Sea
Gulfs Area
Gulf of Aden
North West European Waters
Oman Area of the Arabian Sea
Southern South African Waters