Crude oil, liquid petroleum is a thick, flammable, yellow-to-black mixture of gaseous, liquid, and solid hydrocarbons that occurs naturally beneath the earth's surface, can be separated into fractions including natural gas, gasoline, naphtha, kerosene, fuel and lubricating oils, paraffin wax, and asphalt and is used as raw material for a wide variety of derivative products.
The word petroleum comes from the Latin petra, meaning «rock», and oleum, meaning «oil».
Crude oil that is found accumulated in various porous rock formations in Earth’s crust and is extracted for burning as fuel or for processing into chemical products.
The oil industry classifies «crude» by the location of its origin and by its relative weight or viscosity («light», «intermediate» or «heavy»). The relative content of sulfur in natural oil deposits also results in referring to oil as «sweet», which means it contains relatively little sulfur, or as «sour», which means it contains substantial amounts of sulfur.
Petroleum has mostly been recovered by oil drilling.
Drilling is carried out after studies of structural geology, sedimentary basin analysis, and reservoir characterisation.
Recent improvements to technologies have also led to exploitation of other unconventional reserves such as oil sands and oil shale.
Petroleum exploitation, refining and burning has significant negative environmental and social consequences.
