Proven world oil reserves, 2009.

Petroleum (L. petroleum, from Greek: petra (rock) + Latin: oleum (oil)) or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture ofhydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling. This latter stage comes after studies of structural geology (at the reservoir scale), sedimentary basin analysis, reservoir characterization (mainly in terms of porosity and permeable structures). It is refined and separated, most easily by boiling point, into a large number of consumer products, from gasoline andkerosene to asphalt and chemical reagents used to make plastics and pharmaceuticals. Petroleum is often attributed as the "Mother of all Commodities" because of its importance in the manufacture of a wide variety of materials

Pumpjack pumping an oil well nearLubbock, Texas.

.The term petroleum is found (in the spelling "petraoleum") in tenth-century Old English sources. It was used in the treatise De Natura Fossilium, published in 1546 by the German mineralogist Georg Bauer, also known as Georgius Agricola. In the 19th Century, the term petroleum was frequently used to refer to mineral oils produced by distillation from mined organic solids such as cannel coal (and later oil shale), and refined oils produced from them; in the United Kingdom, storage (and later transport) of these oils were regulated by a series of Petroleum Acts, from the Petroleum Act 1862 c. 66 onward.