Petroleum

Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term petroleum refers both to naturally occurring unprocessed crude oil, as well as to petroleum products that consist of refined crude oil.

Petroleum is a fossil fuel formed over millions of years from anaerobic decay of organic materials from buried prehistoric organisms, particularly planktons and algae. It is estimated that 70% of the world's oil deposits were formed during the Mesozoic, 20% were formed in the Cenozoic, and only 10% were formed in the Paleozoic. Conventional reserves of petroleum are primarily recovered by drilling, which is done after a study of the relevant structural geology, analysis of the sedimentary basin, and characterization of the petroleum reservoir. There are also unconventional reserves such as oil sands and oil shale which are recovered by other means such as fracking.

Once extracted, oil is refined and separated, most easily by distillation, into innumerable products for direct use or use in manufacturing. Petroleum products include fuels such as gasoline (petrol), diesel, kerosene and jet fuel; bitumen, paraffin wax and lubricants; reagents used to make plastics; solvents, textiles, refrigerants, paint, synthetic rubber, fertilizers, pesticides, pharmaceuticals, and thousands of other petrochemicals. Petroleum is used in manufacturing a vast variety of materials essential for modern life, and it is estimated that the world consumes about 100 million barrels (16 million cubic metres) each day. Petroleum production played a key role in industrialization and economic development, especially after the Second Industrial Revolution. Some petroleum-rich countries, known as petrostates, gained significant economic and international influence during the latter half of the 20th century due to their control of oil production and trade.

Petroleum is a non-renewable resource, and its exploitation is damaging to the natural environment, climate system and human health. Extraction, refining and burning of petroleum fuels counteract carbon sinks by releasing large quantities of greenhouse gases back into the Earth's atmosphere, making petroleum a major contributor to anthropogenic climate change. Other negative environmental effects, at almost all stages of use, include direct release—such as oil spills—and secondary pollution of air and water sources.

Proximity to petroleum deposits, and subsequent access to and pricing of oil have historically fueled both domestic and geopolitical conflicts, state-sanctioned oil wars, diplomatic and trade frictions, energy policy disputes and other resource conflicts. While production is estimated to reach peak oil before 2035, global economic focus on climate change mitigation in the transition to renewable energy sources and increased electrification will greatly reduce dependency on petroleum.