Spills can happen on land or water when oil is incorrectly handled, there are railway or truck accidents, tankers or barges collide, the insides of tankers are washed, and when natural oil deposits seep. Sometimes when people change the oil in their cars, they dump the used, dirty oil on the ground or down the storm sewer. The rain carries the oil with the metals and particles from the car engine into streams and creeks. If you added up all the oil dumped on the ground in a year, it would equal or surpass a serious oil tanker spill. Not all spills are man-made.
Crude oil is made by the earth from decayed plants and animals which lived millions of years ago.
Oil has been in the environment for a long time. Some oil lies below the ocean floor and can seep into the ocean through cracks. As much as 1.5 million barrels of oil may enter the ocean from natural seeps each year. When these leaks occur, as when spills occur, natural organisms and chemical processes act to break down the oil over time. This process is called natural bio remediation.