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 latter stage comes after the studies of structural geology, sedimentary basin analysis, reservoir characterization.
It is refined and separated, most easily by
boiling point, into a large number of consumer products, from petrol 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. The use of fossil fuels such as petroleum can have a negative impact on Earth's biosphere, releasing pollutants and greenhouse gases into the air and damaging ecosystems through events such as
oil spills.