Oil tankers are ships of varying sizes designed for the bulk carriage of crude oil and various refined spirits. The largest are up to 650,000 tons.

The current custom is for crude oil to be transported to near its point of use where it is refined as required.

At various times there have been accidents that have led to serious and catastrophic pollution. Another concern has been the pollution caused by careless cleaning of ships' tanks. According to the U.S. Coast Guard, fewer than 67 barrels (about 2,800 gallons) were spilled out of more than 4.2 billion barrels of oil delivered by tankers to the U.S. in 2005. The total volume of oil spilled from tankers annually in the U.S. has averaged fewer than 4,000 barrels annually from 1996-2005, including no marine incidents during 2005's record hurricane season. In fact, far more oil enters the oaceans from natural sources and other incidenrs than from tanker spills,

During World War II, the transport of oil and its products was a critical strategic activity since shortages had a paralysing impact on mechanised nations. The destruction and defence of these ships was therefore of prime concern.

While she was a board member at Chevron, the oil company named a 130,000-ton oil tanker for Condoleezza Rice later United States Secretary of State.

Super Tanker

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 per gallon of gas at the pump.

Due to their size and mass, supertankers have very poor maneuverability; the stopping distance of a supertanker is typically measured in miles. When operating close to the shoreline they are vulnerable to running aground, whether due to mechanical failure, human error or bad weather. When this happens, oil spills are a significant risk. A typical modern supertanker can carry approximately two million barrels of oil. In "single-hulled" tankers, the hull is also the wall of the oil tanks, and any breach will result in an oil spill. Newer tankers are "double-hulled", with a space between the hull and the storage tanks, to reduce the risk of a spill in the event that the outer hull is breached. This space is used to carry water ballast when the ship is not carrying an oil cargo.

Following the Exxon Valdez incident, the United States mandated in the Oil Pollution Act of 1990 (OPA-90) that all supertankers entering United States waters be double-hulled by 2015. The European Union has similar legislation requiring all tankers entering their waters to be double-hulled by 2010. By doing this, incidents like the Exxon Valdez oil spill may possibly be avoided.

The largest double-hulled supertanker in the world is the Hellespont Fairfax. Completed in January 2003, it boasts a deadweight tonnage of 442,470 tonnes.