Organic debris either of animal or plant origin when laid down in sediments under saline conditions is converted by the action of bacteria into a relatively stable product termed neokerogen. During the process of compaction of the sediments, the skin-frictional heat generated by the sedimentary particles sliding over one another decompose the neokerogen into gases and liquids, a considerable proportion of which are unsaturated. These decomposition products travel as films on the surface of the particles. When these films migrate into a more porous zone, the increase of vapor pressure occasioned by passing from the capillary through which the film has been moving into the porous zone results in the liberation of gases which accumulate in the porous zone. Here the gases and the liquids associated with them are converted into petroleum by the catalytic action of the oxide surfaces of the sediments acting through geologic time.