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Name: Lisa D.
Status: educator
Age: 20s
Location: N/A
Country: N/A
Date: Sunday, December 08, 2002

What is the chemical composition of oil? I know there could be many answers to this question. I am looking for the common make-up of the oil we would see in an oil spill (like Exxon Valdez, etc.).


Crude oil, like that found in the spills to which you refer, is a very complex mixture of compounds composed of (mainly) carbon, hydrogen, oxygen, and sulfur. Of these elements, carbon and hydrogen are by far the major components. Linked together with inter-atom bonds, these CH compounds form a dazzling variety of different kinds of molecules of many different shapes and sizes. Collectively, these carbon-hydrogen compounds are referred to as "hydrocarbons."

The smallest hydrocarbons are gaseous at ordinary room temperature. The somewhat larger hydrocarbon molecules are liquids, whereas the largest are solids. Of course in crude oil, all these different kinds of molecules are "dissolved" in each other -- making for a rather unpleasant looking and smelling mess.

Transported to a refinery, the various "fractions" of the crude oil (gases, liquids, and solids) are separated from each other (and sometimes modified in composition) before they are distributed for use. Obviously, the liquid fractions are primary components of gasoline, diesel fuel, and lubricating and heating oils. The very large hydrocarbon components are solids at room temperature and are used for roofing and road surfaces -- tar and asphalt.

ProfHoff 540

As you suggest, the composition of crude oil is very complex. In addition, the composition depends upon the source. This "fingerprint" can be used to identify the origin of a crude. The following web site offers some information regarding the composition of a "generic" crude oil.

Vince Calder

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