Petroleum or
crude oil, is a naturally occurring
flammable liquid consisting of a complex mixture of
hydrocarbons of various molecular weights and other liquid
organic compounds, that are found in
geologic formations beneath the
Earth's surface. A
fossil fuel, it is formed when large quantities of dead organisms, usually
zooplankton and
algae, are buried underneath
sedimentary rock and undergo intense heat and pressure.
Petroleum is recovered mostly through
oil drilling. This comes after the 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
petrol (or
gasoline) and
kerosene to
asphalt and chemical
reagents used to make
plastics and
pharmaceuticals. Petroleum is used in manufacturing a wide variety of materials, and it is estimated that the world consumes about 88 million barrels each day.