|A supertanker is an unofficial nickname that applies to a certain class of tanker ship built to transport very large quantities of liquids; in practice this typically refers to crude oil. Supertankers are usually considered to be Very-Large Crude Carriers (VLCC) and Ultra-Large Crude Carriers (ULCC).|
Tanker ships above 250,000 tonnes deadweight tonnage are generally considered supertankers. They are the largest ships in the world, larger even than supercarriers; the largest of which is the Knock Nevis, weighing in at 647,955 tonnes fully laden. When first introduced, their size and draft prevented them from docking at many existing docks, requiring them to discharge their cargo into smaller tankers offshore. Some ports have developed special deep-water off-loading facilities connected to the land by pipelines (for an example, see Louisiana Offshore Oil Port). Supertankers are also very efficient ships, relying on a single propeller for propulsion, and typically account for only US $0.02 of the cost of gas at the pump.