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

Exxon Valdez incident

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 old Regulation 13F - (now Regulation 19) 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 (now Regulation 20), 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 incident

The sinking of the Erika off the coast of France in December 1999 led to a new, accelerated phase-out schedule for single-hull tankers - the revision of old regulation 13G of MARPOL.
The investigations into the Erika incident carried out by the French government and the Maltese maritime authority concluded that age, corrosion, insufficient maintenance and inadequate surveys were all strong contributing factors to the structural failure of the ship.

There was a wide consensus that the Erika and other the recent accidents involving oil tankers pointed to a need for additional international measures to eradicate substandard vessels, particularly substandard oil tankers given the catastrophic impact such ships may have on the marine environment in the case of an accident.

Besides the revised phase-out scheme for single-hull tankers, IMO also adopted other measures in response to the incident:
  • Amendments adopted by IMO in October 2000 to raise by 50 percent the limits of compensation payable to victims of   pollution by oil from oil tankers under the International Convention on Civil Liability for Oil Pollution Damage (CLC Convention) and the International Convention on the Establishment of an International Fund for Compensation for Oil Pollution Damage (IOPC Fund). 
  • IMO's Maritime Safety Committee (MSC) in December 2000 adopted amendments to the guidelines on the enhanced programme of inspections during surveys of bulk carriers and oil tankers (resolution A.744(18)) with relation to the evaluation of the longitudinal strength of the hull girder of oil tankers.
  • Furthermore, IMO has taken action on several other operational matters based on a list of measures aimed at enhancing safety and minimizing the risk of oil pollution, drawn up in response to the Erika incident. 

The Prestige incident

The Prestige incident of November 2002 led to further calls for amendments to the phase-out schedule for single hull tankers.
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.