Prevention of Pollution by Oil

Oil tankers transport some 1,800 million tonnes of crude oil around the world by sea including 50 percent of U.S. oil imports (crude oil and refined products).  Most of the time, oil is transported quietly and safely.

Measures introduced by IMO have helped ensure that the majority of oil tankers are safely built and operated and are constructed to reduce the amount of oil spilled in the event of an accident. Operational pollution, such as from routine tank cleaning operations, has also been cut.

The most important regulations for preventing pollution by oil from ships are contained in Annex I of the International Convention for the Prevention of Pollution from Ships, 1973, as modified by the Protocol of 1978 relating thereto (MARPOL 73/78), The International Convention for the Safety of Life at Sea  (SOLAS), 1974 also includes special requirements for tankers.

In this section:

Oil pollution – background

Torrey Canyon disaster

1973 International Convention for the Prevention of Pollution from Ships

1978 Conference on Tanker Safety and Pollution Prevention

Exxon Valdez disaster

1992 “double hull” amendments

The Erika disaster and revised single-hull phaseout schedule

The Prestige disaster

Revised MARPOL Annex I - entry into force 1 January 2007

Further Information

Oil pollution – background

The world's first oil tankers appeared in the late 19th century and carried kerosene for lighting, but the invention of the motor car fuelled demand for oil. During the Second World War, the standard oil tanker was the T2, 16,400 tonnes deadweight, but tankers grew rapidly in size from the 1950s onwards.

The first 100,000-tonne crude oil tanker was delivered in 1959 to cover the route from the Middle East to Europe round the Cape of Good Hope (thereby avoiding the Suez Canal which had been temporarily closed following political conflicts in 1956). Shippers saw economies of scale in larger tankers and by the mid-1960s, tankers of 200,000 tonnes deadweight- the Very Large Crude Carrier or VLCC - had been ordered. 

The potential for oil to pollute the marine environment was recognised by the International Convention for the Prevention of Pollution of the Sea by Oil, 1954 (OILPOL 1954). The Conference adopting the Convention was organised by the United Kingdom government, and the Convention provided for certain functions to be undertaken by IMO when it came into being. In fact, the Convention establishing IMO entered into force in 1958 just a few months before the OILPOL convention entered into force, so IMO effectively managed OILPOL from the start, initially through its Maritime Safety Committee.

The OILPOL Convention recognised that most oil pollution resulted from routine shipboard operations   such as the cleaning of cargo tanks.  In the 1950s, the normal practice was simply to wash the tanks out with water and then pump the resulting mixture of oil and water into the sea.     

OILPOL 54   prohibited the dumping of oily wastes within a certain distance from land and in 'special areas' where the danger to the environment was especially acute.  In 1962 the limits were extended by means of an amendment adopted at a conference organised by IMO.

Meanwhile, IMO in 1965, set up a Subcommittee on Oil Pollution, under the auspices of its Maritime Safety committee, to address oil pollution issues.

Torrey Canyon disaster

Although the OILPOL Convention had been ratified, pollution control was at the time still a minor concern for IMO, and indeed the world was only beginning to wake up to the environmental consequences of an increasingly industrialised society.

But in 1967, the Torrey Canyon ran aground while entering the English Channel and spilled her entire cargo of 120,000 tons of crude oil into the sea.  This resulted in the biggest oil pollution incident ever recorded up to that time.  The incident raised questions about measures then in place to prevent oil pollution from ships and also exposed deficiencies in the existing system for providing compensation following accidents at sea.

It was essentially this incident that set in motion the chain of events that eventually led to the adoption of MARPOL - as well as a host of Conventions in the field of liability and compensation.

First, IMO called an Extraordinary session of its Council, which drew up a plan of action on technical and legal aspects of the Torrey Canyon incident.

It was still recognized, however, that although accidental pollution was spectacular, operational pollution was the bigger threat.

In 1969, therefore, the 1954 OILPOL Convention was again amended, this time to introduce a procedure known as 'load on top' which had been developed by the oil industry and had the double advantage of saving oil and reducing pollution.  Under the system, the washings resulting from tank cleaning are pumped into a special tank.  During the voyage back to the loading terminal the oil and water separate.  The water at the bottom of the tank is pumped overboard and at the terminal oil is pumped on to the oil left in the tank.

At the same time, the enormous growth in the maritime transport of oil and the size of tankers, the increasing amount of chemicals being carried at sea and a growing concern for the world's environment as a whole, made many countries feel that the 1954 OILPOL Convention was no longer adequate, despite the various amendments which had been adopted.

In 1969, the IMO Assembly decided to convene an international conference to adopt a completely new convention, which would incorporate the regulations contained in OILPOL 1954 (as amended).  At the same time, the Sub-Committee on Oil Pollution was renamed the Sub-Committee on Marine Pollution, to broaden its scope, and this became the Marine Environment Protection Committee (MEPC), which was eventually given the same standing as the Maritime Safety Committee, with a brief to deal with all matters relating to marine pollution.

The conference was set for October-November 1973, and preparatory meetings began in 1970.

Meanwhile, in 1971 IMO adopted amendments to OILPOL 1954, which limited the size of cargo tanks in all tankers ordered after 1972. The intention was that given certain damage to the vessel, only a limited amount of oil could enter the sea.

1973 International Convention for the Prevention of Pollution from Ships

The 1973 conference in October-November 1973 incorporated much of OILPOL 1954 and its amendments into Annex I, covering oil, while other annexes covered chemicals, harmful substances carried in packaged form, sewage and garbage.

Annex I expanded and improved on OILPOL in several ways. It specified requirements for continuous monitoring of oily water discharges and included the requirement for Governments to provide shore reception and treatment facilities at oil terminals and ports. It also established a number of Special Areas in which more stringent discharge standards were applicable, including the Mediterranean, Red Sea and Gulf, and Baltic Seas. These special areas would be implemented when the littoral States concerned had provided adequate reception facilities for dirty ballast and other oily residues.

 An important regulation of Annex I was Regulation 13 which required segregated  ballast tanks on new tankers over 70,000 deadweight tonnes.   The aim was to ensure that ballast water (taken on board to maintain stability, such as when a tanker is sailing empty to pick up cargo) is never going to be contaminated by oil carried as cargo or fuel.

As it turned out, there was slow progress at ratifying the Convention (partly due to technical problems in ratifying Annex II) and the non-ratification of MARPOL became a major concern.

At the same time, a series of tanker accidents in 1976-1977, mostly in or near United States waters and including the stranding of the Argo Merchant, led to demands for more stringent action to curb accidental and operational oil pollution. The Argo Merchant ran aground off Massachussetts in December 1976. It was a small tanker, carrying 27,000 tons of oil, but caused huge public concern as the oil slick threatened New England resorts and Georges Bank fishing ground.

The United States took the lead in asking the IMO Council, in May 1977, to consider adopting further regulations on tanker safety. The Council agreed to convene a Conference in February 1978 - the Conference on Tanker Safety and Pollution Prevention. 

A working group met in May, June and July, and a combined MSC/MEPC met in October, to prepare basic documents for the Conference.

1978 Conference on Tanker Safety and Pollution Prevention

The Conference, in February 1978, adopted a protocol to the 1973 MARPOL Convention, absorbing the parent Convention and expanding on the requirements for tankers to help make them less likely to pollute the marine environment.

The Protocol expanded the requirements for segregated ballast tanks to all new crude oil tankers of 20,000 dwt and above and all new product carriers of 30,000 dwt and above. The Protocol also required segregated ballast tanks to be protectively located, in other words, placed in areas of the ship where they will minimise the possibility of and amount of oil outflow from cargo tanks after a collision or grounding.

New tankers over 20,000 dwt were required to be fitted with crude oil washing system. Crude oil washing, or COW, is the cleaning or washing of cargo tanks with high-pressure jets of crude oil. This reduces the quantity of oil remaining on board after discharge.

The Protocol also called for existing tankers over 40,000 dwt to be fitted with either segregated ballast tanks or crude oil washing systems; while for an interim period, it also allowed for some tankers to use clean ballast tanks, whereby specific cargo tanks are dedicated to carry ballast water only.

Additional measures for tanker safety were incorporated into the 1978 Protocol to the International Convention for the Safety of Life at Sea (SOLAS), 1974. These included the requirement for inert gas systems (whereby exhaust gases, which are low in oxygen and thus incombustible, are used to replace flammable gases in tanks) on all new tankers over 20,000 dwt and specified existing tankers. The SOLAS Protocol also included requirements for steering gear of tankers; stricter requirements for carrying of radar and collision avoidance aids; and stricter regimes for surveys and certification.

In order to speed up implementation of MARPOL, the Conference allowed that the Parties "shall not be bound by the provisions of Annex II of the Convention for a period of three years" from the date of entry into force of the Protocol, so that countries could accept Annex I and have three years to implement Annex II.

Both the 1978 MARPOL and SOLAS Protocols were seen as major steps in raising construction and equipment standards for tankers through more stringent regulations.

If the world needed further reminder of the need for strict regimes to control oil pollution, it got it just one month after the 1978 Conference, when the Amoco Cadiz ran aground off Brittany, giving France its worst oil spill ever. The tanker, filled with 223,000 tons of crude oil, lost its entire cargo, covering more than 130 beaches in oil. In places, the oil was up to 30 cm thick.

Sufficient States had ratified MARPOL by October 1982, and the MARPOL 1973/78 Convention entered into force on 2 October 1983.

Since the Convention entered into force, there have been a number of amendments to the Convention – see MARPOL 73/78.

Exxon Valdez disaster

It was another tanker accident which led to one of the most important changes to be made to Annex I of the Convention since the adoption of the 1978 Protocol.

In March 1989, the Exxon Valdez, loaded with 1,264,155 barrels of crude oil, ran aground in the northeastern portion of Prince William Sound, spilling about one-fifth of its cargo. It was the largest crude spill, to date, in US waters and - probably the one which gained the biggest media coverage to date. The U.S. public demanded action - and duly got it.

The United States introduced its Oil Pollution Act of 1990 (OPA 90), making it mandatory for all tankers calling at U.S. ports to have double hulls.

The United States also came to IMO, calling for double hulls this time to be made a mandatory requirement of MARPOL. The implications of the Exxon Valdez spill were not lost on IMO Members, and the MEPC began discussions on how the U.S. proposals could be implemented.

As on previous occasions, there was some resistance on the part of the oil industry  to  double hulls  being  made mandatory,  due mainly to the cost of retrofitting existing tankers.

At the same time, several of IMO's Member States said that other designs should be accepted as equivalents and that measures for existing ships should also be contemplated.  In 1991 a major study into the comparative performances of the double-hull and mid-height deck tanker designs was carried out by IMO, with funding from the oil and tanker industry.

It concluded in January 1992 that the two designs could be considered as equivalent, although each gives better or worse outflow performance under certain conditions.

Eventually, the MEPC agreed to make mandatory double hulls or alternative designs "provided that such methods ensure the same level of protection against pollution in the event of a collision or stranding".  These design methods must be approved by the MEPC.

1992 “double hull” amendments

The amendments introducing double hulls (or an alternative) were contained in Regulation 13F - prevention of oil pollution in the event of collision or stranding. The amendments were adopted in March 1992 and entered into force in July 1993.

Regulation 13F applies to new tankers - defined as delivered on or after 6 July 1996 - while existing tankers must comply with the requirements of 13F not later than 30 years after their date of delivery.

Tankers of 5,000 dwt and above must be fitted with double bottoms and wing tanks extending the full depth of the ship's side.  The regulation allows mid-deck height tankers with double-sided hulls as an alternative to double hull construction.

Oil tankers of 600 dwt and above but less than 5,000 dwt, must be fitted with double bottom tanks and the capacity of each cargo tank is limited to 700 cubic metres, unless they are fitted with double hulls.

The MEPC also adopted Regulation 13G, concerned with existing tankers, which  makes provision for an enhanced programme of inspections to be implemented, particularly for tankers more than five years old.

Regulation 13G also allowed for future acceptance of other structural or operational arrangements - such as hydrostatic balance loading (HBL) - as alternatives to the protective measures in the Regulation.

The Erika disaster and revised single-hull phaseout schedule

On 12 December 1999 the 37,238-dwt tanker Erika broke in two in heavy seas off the coast of Brittany, France, while carrying approximately 30,000 tonnes of heavy fuel oil. Although the crew were saved, some 14,000 tonnes of oil were spilled and more than 100 miles of Atlantic coastline were polluted.

As a result of the Erika disaster, proposals were submitted to the MEPC to accelerate the phase-out of single-hull tankers contained in the 1992 MARPOL amendments.

The amendments to Regulation 13G in Annex I of MARPOL 73/78 were adopted by the MEPC’s 46th session in April 2001.

The Prestige disaster

The Prestige tanker incident of 2002 led to calls for further changes to MARPOL 73/78. The MEPC at its 49th session in July 2003 agreed to an extra session of the Committee, to be convened in December 2003, to consider the adoption of proposals for an accelerated phase-out scheme for single hull tankers, along with other measures including an extended application of the Condition Assessment Scheme (CAS) for tankers.

Revised MARPOL Annex I

The revised MARPOL Annex I Regulations for the prevention of pollution by oil was adopted in October 2004 and enters into force on 1 January 2007. It incorporates the various amendments adopted since MARPOL entered into force in 1983, including the amended regulation 13G (regulation 20 in the revised annex) and regulation 13H (regulation 21 in the revised annex) on the phasing-in of double hull requirements for oil tankers. It also separates, in different chapters, the construction and equipment provisions from the operational requirements and makes clear the distinctions between the requirements for new ships and those for existing ships. The revision provides a more user-friendly, simplified Annex I.

New requirements in the revised Annex I include the following:

  • Regulation 22 Pump-room bottom protection: on oil tankers of 5,000 tonnes deadweight and above constructed on or after 1 January 2007, the pump-room shall be provided with a double bottom.
  • Regulation 23 Accidental oil outflow performance - applicable to oil tankers delivered on or after [date of entry into force of revised Annex I plus 36 months] 1 January 2010; construction requirements to provide adequate protection against oil pollution in the event of stranding or collision.

Oman Sea - new special area under MARPOL Annex I
The Oman Sea area of the Arabian Seas is designated a special area in the revised Annex I.

The other special areas in Annex I are: Mediterranean Sea area; Baltic Sea area; Black Sea area; Red Sea area; "Gulfs" area; Gulf of Aden area; Antarctic area; and North West European Waters. In the special areas, there are stricter controls on discharge of oily wastes.

Further Information

Tanker safety - preventing accidental pollution

Responding to oil spills

MARPOL 73/78

Information Resources on current topics

Information Resources on the Prestige

Focus papers

MARPOL - 25 years

Preventing marine pollution

Tanker safety: the work of the International Maritime Organization


Marine Environment
Prevention of Pollution
Oil Pollution
SOPEP/Shipboard Marine Pollution Emergency Plans
Tanker safety
Cross reference between old and new MARPOL Annex I
Ship-to-ship oil transfer
Oil fuel tank protection
IGC Code
Oil tankers - regulation 20/21 implementation