The process of natural gas and crude oil formation took several million years to complete. During the earth‘s history, large numbers of micro-organisms, bacteria, and algae, collectively known as plankton, lived in the earth‘s oceans and lakes. As it died off, the plankton sank to the bottom of the lake or sea, where it became mixed with clay and lime mud deposits. If the organic matter was buried so rapidly that the oxygen supply needed for natural decay was cut off, source rock was formed, the starting material for oil and gas.

In the course of the earth‘s history, further layers of sediment were deposited on top of the source rock. The weight of the layers deposited on top of the source rock and the constant motion of the earth‘s crust buried the source rock increasingly deeper. Thus buried several thousand meters below, the pressure rose on the rock layer with the trapped organic matter, as well as its density and temperature. Temperatures of between 60 and 120°C led to the formation of organic crude oil. Where the source rock was exposed to temperatures of more than 150°C, the oil‘s long-chain molecules split up and formed natural gas.

However, most natural gas was formed from source rock with a high proportion of higher land plants. Especially in shallow coastal regions, frequent rises and falls in the sea level cause deposits to alternate with clay and sandstone. The natural carbonization process turned the plant matter successively into peat, lignite, and finally bituminous coal and anthracite, the source rock for natural gas.