Oil tankers are ocean-going ships used to transport oil around the world. Often controversial, these huge vessels have been the cause of environmental damage, but fulfil a vital role in the transportation of essential fossil fuels.

Volume

Oil tankers carry 2.4 billion tons of oil per year, accounting for two-thirds of the global trade in oil, according to Reuters. Tankers come in six sizes, ranging from 10,000 deadweight tons (dwt) up to 300,000 dwt or higher. Larger vessels tend to carry crude oil, while smaller ships are used for refined products like gasoline.

Safety

Modern tankers have two hulls in order to lessen the chance of a collision causing oil to leak into the sea. Single-hulled vessels are gradually being phased out, with 2010 being the target date for ending their use. The world's largest tanker, the single-hulled Knock Nevis, was retired in 2010.

Spills

The most damaging oil tanker disaster, the Exxon Valdez spill, led to the release of up to 46 million gallons of crude oil into the wildlife-rich seas around Prince William Sound in Alaska. The largest spill resulted from the 1979 collision near Tobago between two very large oil tankers, the Atlantic Empress and the Aegean Captain, which released 280,000 tons of oil.