Gallons: 240 to 336 million
How It Happened:
As Iraqi forces retreated from Kuwait during the first Gulf War, they opened the valves of oil wells and pipelines in a bid to slow the onslaught of American troops. The result was the largest oil spill history has seen. Some 240 million gallons of crude oil flowed into the Persian Gulf. The resulting oil slick spanned an area just larger than the size of the island of Hawaii.