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Composition

Crude oil also contains other organic compounds with nitrogen, oxygen and sulfur, and traces of metals such as iron, nickel, copper and vanadium. The molecular composition of crude oil varies widely from formation to formation. The proportion of light hydrocarbons in a petroleum mixture varies among oil fields. Crude oil may be broadly characterized as paraffinic or naphthenic. On average, crude oil is made of about 30 percent alkanes, 49 percent naphthenes, 15 percent aromatics and 6 percent asphaltics by weight.

Hydrocarbon fractions

The alkanes from pentane (C₅H₁₂) to octane (C₈H₁₈) are refined into gasoline. Alkanes with more than 16 carbon atoms can be refined into fuel oil and lubricating oil. Paraffin wax is an alkane with approximately 25 carbon atoms, while asphalt has 35 and up. The aromatic hydrocarbons are unsaturated hydrocarbons that have one or more benzene rings.

Light fractions and derived oils

Petroleum ether is the petroleum fraction consisting of aliphatic hydrocarbons and boiling in the range 35-60 °C, and it is commonly used as a laboratory solvent. Despite the name, petroleum ether is not an ether. Petroleum ether has a gasoline- or kerosene-like odor. Mineral oil, a colorless and odorless mixture of higher alkanes, is particularly a distillate of petroleum.

Name and economic role

The word petrol derives from the Medieval Latin word petroleum, from petra, rock, and oleum, oil. Petroleum is a portable, dense energy source that powers the vast majority of vehicles and is the base of many industrial chemicals. Petroleum makes up 38 percent of total energy consumption in the United States, but is responsible for only 0.4 percent of electricity generation.

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