Oil refining is a process used to separate crude oil into useable components. Crude oil is also known as petroleum, a term which comes from the Latin words for rock and oil. Petroleum is a complex mixture of hydrocarbon compounds, usually containing impurities such as nitrogen, oxygen, sulfur, and small quantities of trace metals. Gasoline, diesel fuel, heating oils, lubricants, waxes, asphalt and coke are obtained from refined oil.

Crude oil is the product of millions of years of decay of organic materials, such as plant life. Oil migrates upward through fissures in the ground and until it eventually reaches a solid layer of rock, where becomes trapped underneath in a reservoir. These arched layers of rock that trap oil are known as anticlines. Petroleum can also be trapped by fractured rock layers, salt formations, and stratigraphic traps. Some oil is also contained in shales and...