Overview:

Petroleum is a mixture of liquid hydrocarbons (chemical compounds containing only hydrogen and carbon) plus various impurities such as sulfur. Unprocessed petroleum is usually called crude oil, although it has been called mineral oil and Seneca oil, named for the Seneca Indians of Western Pennsylvania. The name petroleum is from a combination of Latin words meaning "rock oil". We refer to it here simply as oil.

As found in the earth, oil may have a variety of properties. Some forms are black, others dark green, and some light like kerosene. The liquid ranges from very viscous to easy-flowing. Crude oil usually consists of a mixture of hydrocarbons having varying molecular weights and differing from one another in structure and properties. These various species are separated into groups, or fractions, by a process of distillation called refining. Oil fuel, in all of its usable forms, is a refined product, unlike coal and natural gas which can often be burned in their natural condition.

Use the underlined links above to go to pages of tutorials and links for the various aspects of oil listed.