Crude oil is a limited resource. It is estimated that there is a total of 2,390 billion barels of crude oil on Earth. Estimates of undiscovered reserves range from 275 to 1,469 billion barrels.

About 77% of crude oil has already been discovered, and 30% of it has been used so far. From 1859-1968 200 billion barels of oil have been used, and since then oil production has stabilized to 22 billion barels per year. It is estimated that oil reserves will become scarce by 2050s.

Most of oil is concentrated in the Near East - around 41%. North America, Russia, and Antarctica are also rich in crude oil.

See also: List of oil fields, Petroleum