It is customary to refer to unprocessed oil as crude oil. A viscous oily liquid with a dark brown color and a green scent with a distinctive odor. It is a mixture of various liquid hydrocarbons such as alkanes, cycloalkanes, aromatic hydrocarbons and olefins.

The main components are carbon and hydrogen, accounting for 83-87% and 11-14% respectively; there are also a small amount of sulfur, oxygen, nitrogen and trace amounts of phosphorus, arsenic, potassium, sodium, calcium, magnesium, nickel, iron, Elements such as vanadium. The specific gravity is 0.78 to 0.97, the molecular weight is 280 to 300, and the freezing point is -50 to 24 °C. Through refining and processing, crude oil can be obtained from various fuel oils, solvent oils, lubricating oils, greases, paraffin, asphalt, liquefied gases, aromatic hydrocarbons, etc., providing fuel, raw materials and chemical products to various sectors of the national economy.

On October 27, 2017, the list of carcinogens published by the World Health Organization's International Agency for Research on Cancer was initially compiled. Crude oil is listed in the list of three types of carcinogens.