The Exxon Valdez spill in Alaska was approximately 11 million gallons. That spill was only about the 35th largest in the world, though it was the largest in the US. It came from a huge supertanker that was about the size of 15 gyms in length X 4 gyms wide X 2 gyms deep (which held 66 million gallons).
Every day 31.5 billion gallons of oil are at sea being transported. But not all spills come from tankers. Some comes from storage tanks, pipelines, oil wells, tankers and vessels cleaning out tanks.
A good experiment to do here is to add vegetable oil, which acts like crude oil, to food-colored water in a large, clear plastic soda bottle with a cap. Shake it and watch how the oil always settles on top.
30-40% evaporates in the first 24-48 hours; these are the most poisonous (toxic) portions, as well as the portions that are the most soluble, and flammable.
Oil tends to float and spread out into a very thin film on the water surface...usually only about 0.1 mm thick...then spreads even thinner to a sheen, which is one tenth or one one-hundredth of this. Sheens are often seen as rainbow-like or silvery in puddles in parking lots.
It is very rare for oil to sink. It needs to adhere to heavier particles such as sand, algae, or silt to sink. An exception is a kind of oil used for burning in electric utility plants. This oil can actually sink in water since it is heavier than water.
These impacts are very often grossly exaggerated in the public media. Environmentalist groups have been notorious in spreading misinformation about environmental effects. Nevertheless, oil can have a significant impact on marine larvae, birds and mammals in particular, and to a lesser extent on fish.
Some components of oil are toxic if exposure occurs within the first two days of a spill (1 part per million [ppm], i.e. one gallon in one million gallons, can be toxic to invertebrate larvae; 1000 ppm for fish). Oil on feathers hinders the water-repellancy of the bird. Oil on fur takes away its insulating capacities.
Information provided by:
Oil Spill Intelligence Report, Arlington, MA, U.S.A.