Petroleum (L. petroleum, from early 15c. "petroleum, rock oil" (mid-14c. in Anglo-French), from Medieval Latin petroleum, from Latin petra rock(see petrous) + Latin: oleum oil (see oil (n.)).) is a naturally occurring, yellow-to-black liquid found in geologic formations Inside the Earth's surface, which is usually refined into many kinds of fuels. It consists of hydrocarbons of various molecular weights and other compounds. The name petroleum covers both naturally occurring unprocessed crude oil and petroleum products that are made of refined crude oil. A fossil fuel, petroleum is made when huge quantities of dead organisms, usually zooplankton and algae, are buried inside sedimentary rock and subjected to intense heat and pressure.
Petroleum is recovered usually through oil drilling (natural petroleum springs are rare). This comes after the research of structural geology (at the reservoir scale), sedimentary basin analysis, reservoir characterization (mainly in terms of the porosity and permeability of geologic reservoir structures). It is refined and separated, most easily by distillation, into a huge number of consumer products, from gasoline (petrol) and kerosene to asphalt and chemical reagents used to make plastics and pharmaceuticals , road construction . Petroleum is used in manufacturing a wide variety of materials, and it is estimated that the world consumes about 90 million barrels each day.
Concern over the depletion of the earth's finite reserves of oil, and the effect this would have on a society dependent on it, is a concept known as peak oil. The use of fossil fuels, such as petroleum, has a negative impact on Earth's biosphere, damaging ecosystems through events such as oil spills and releasing a range of pollutants into the air including ground-level ozone and sulfur dioxide from sulfur impurities in fossil fuels.