Oil is a mixture of hydrocarbons usually existing
in the liquid state in natural underground pools or reservoirs. In its
natural state, called crude oil, it remains liquid at atmospheric pressure
after passing through surface separating facilities. Depending upon the
characteristics of the crude stream, it may also include:
Liquids produced at natural gas processing plants are excluded. Crude oil
is refined to produce a wide array of petroleum products, including heating
oils; gasoline, diesel and jet fuels; lubricants; asphalt; ethane, propane,
and butane; and many other products used for their energy or chemical content.
- Small amounts of hydrocarbons that exist in gaseous phase in natural
underground reservoirs but are liquid at atmospheric pressure after
being recovered from oil well (casinghead) gas in lease separators and
are subsequently commingled with the crude stream without being separately
measured. Lease condensate recovered as a liquid from natural gas wells
in lease or field separation facilities and later mixed into the crude
stream is also included;
- Small amounts of non-hydrocarbons produced with the oil, such as sulfur
and various metals;
- Drip gases, and liquid hydrocarbons produced from tar sands, oil sands,
gilsonite, and oil shale.
Natural gas is often found
in association with oil.