Causes of accidents

According to insurers’ statistics, 80% of oil tanker accidents which cause oil spills at sea are a result of human errors: badly handled manoeuvres, neglected maintenance, insufficient checking of systems, lack of communication between crew members, fatigue, or an inadequate response to a minor incident causing it to escalate into a major accident. From a more practical point of view, analysis of the circumstances surrounding accidents (see animation “Causes of oil tanker accidents”) demonstrates the high proportion of spills due to groundings and collisions.

Wreck of the Aegean Sea by La Coruña, Spain

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ITOPF is a mutual organisation providing technical advice on pollution response for shipowners of oil tankers. ITOPF experts contribute to response operation management, impact assessment and environmental restoration operations around the world. See below the home page of ITOPF’s website, which is an indispensable source of information on accidents, their causes and response carried out.

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Collisions are generally due to manoeuvring errors, especially in poor visibility and/or busy shipping traffic areas. Groundings are also often a result of manoeuvring errors, often made worse by high winds, challenging currents and bad weather.


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Causes of oil tanker accidents (spills of over 700 tonnes)

The grounding of the Sea Empress at the entrance to Milford Haven port, Wales (Great Britain) is one such example. However, equipment failure is a more common cause of groundings than of collisions. The grounding of the oil tanker the Braer in the Shetland Islands, Scotland (Great Britain), resulting from seawater entering into a fuel tank, causing engine failure, is a classic example of technical failure.

Oil tanker spills

The International Tanker Owners Pollution Federation Ltd keeps an up-to-date database on the Internet (, on oil spills of over 700 tonnes, from oil tankers, ore carriers and tank barges which have occurred all over the world since 1967. Information is also provided on various aspects of the spills and their consequences.

This data brings to light the fact that a little more than 5.5 million tonnes of oil were spilled in the world’s seas by oil tanker accidents during the 30 year period from 1970-2000, totalling nearly 182,000 tonnes per year with a peak of 640,000 tonnes in 1979. Since then, despite a bad year in 1991, the tendency is towards a considerable decrease. In the decade from 1990 to 1999, 73% (830,000 tonnes) of the total amount spilled (1,140,000) was caused by only 10 accidents.

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Number of oil tanker accidents causing spills of over 700 tonnes