Petroleum, or crude oil, consists of hydrocarbons covering a wide range of boiling points and molecular weights. Although compositional analysis is usually taken to C20, crude oil is best visualized as a smooth continuous gradation of boiling point matter up to approximately C100. The relative quantities of the many thousands between geographical location and the composition of the crude oil.
Petroleum is found as an accumulation of hydrocarbons in porous sedimentary rocks ranging in age from ten to several hundred million years old. It is believed that petroleum originates from anaerobic decomposition of constituents of marine life, plankton and algae leading to the formation of organic clays which, when subject to pressure, temperatures up to 300°C and geological time, form petroleum.
In the petroleum industry, oil density is traditionally measured according to an inverse scale derived by the American Petroleum Institute, known as the API gravity. The relationship with specific gravity, measured at 60°F (15.6°C) is according to the following equation: Density = (141.5/SG60) − 131.5. Crude oil density ranges from approximately 800.0 to 930.0 kg/m3 (45.3-20.6 degrees API.).