petroleum

Petroleum, also called crude oil, is a naturally occurring, liquid mixture of hydrocarbons and small amounts of organic compounds. It occurs in porous rock formations, often in reservoirs capped by impermeable layers, and is extracted by drilling. Petroleum is a major energy source and a key feedstock for the chemical industry.

Crude oil composition varies by source but typically includes alkanes, cycloalkanes, aromatics, and heteroatomic compounds such as sulfur, nitrogen, and trace metals. The density and viscosity, often expressed as API gravity, influence processing and end-use applications.

Formation occurs over millions of years from the remains of microscopic organisms deposited in sediments. Through heat and pressure, organic matter is transformed into kerogen and then into liquid hydrocarbons that migrate into porous reservoirs.

Extraction involves drilling wells to reach reservoirs. Primary production relies on natural pressure or pumping; secondary methods such as water flooding; and tertiary or enhanced oil recovery techniques, including steam, solvents, or CO2 injection, to increase yield.

Crude oil is refined by distillation and further processing to produce fuels, lubricants, and petrochemicals. Major refining steps include cracking, reforming, hydrocracking, and alkylation. Byproducts include asphalt, waxes, and feedstock for chemical industries.

Petroleum products power transportation, heating, and industrial processes, and serve as feedstocks for plastics, synthetic fibers, and chemicals. Transportation of crude and refined products relies on pipelines, ships, rail, and trucks.

Environmental and social considerations include greenhouse gas emissions from combustion, air pollutants, spills, and land use. Refining and transport pose risks; regulation, technology improvements, and transition strategies aim to reduce environmental impact.

Historically, petroleum use expanded rapidly after the industrial revolution. Global markets are influenced by exploration, production, geopolitics, and policy. Proven reserves are estimated by geological surveys and industry assessments and are subject to change with new discoveries and technology.