A Ship which has a capacity between 100,000 and 400,000 displacement tons or deadweight tons (dwt). AKA Very Large Crude Carrier (VLCC). A supertanker with a capacity over 500,000 dwt is called an Ultra Large Crude Carrier (ULCC). They are used for transporting crude oil and other liquids in large quantities. The control of this ship is so unweildy that any action taken by the captain will not affect the ship for 15 minutes. The deck is 952 feet long, and 166 feet wide, its large enough to hold three football fields.
The advantage of using these big tankers is much lower cost per unit moved.
80% of the world's oil tankers still have single hulls. There is a law requiring ship owners to retire these vessels when they reach a certain age and replace them with double hulled boats.
The Exxon Valdez which ran aground in Prince William Sound in Alaska was a supertanker. This resulted in the passage of the Oil Spill Act of 1990.