As their name suggests, tankers are mammoth floating tanks that transport liquid cargo such as petroleum and natural gas. A tanker has several individual compartments inside the main body, allowing it to carry thousands of tons of petroleum. Under the Oil Pollution Act of 1990, passed by the United States Congress, tankers with single hulls are to be gradually phased out and replaced by double-hulled tankers. Single-hulled tankers have been responsible for devastating oil spills that have polluted beaches and killed marine life. Under the legislation, only tankers with double hulls will be able to enter U.S. waters by the year 2015.
The increasing global dependence on petroleum products-from gasoline, kerosene, and diesel to plastics and chemicals-has made petroleum tankers the largest ships afloat.
The world's tanker fleet doubled in number and tripled in tonnage between 1939 and 1959. Tankers are essentially giant holding tanks, or sometimes a series of tanks, shaped like ships and powered by engines. They are equipped with sophisticated piping systems for loading and unloading their contents, fire control systems, navigation equipment, control rooms, and crew quarters.