The most stable portions of organic tissues are fatty acids. It is assumed petroleum is formed from a wax-like substance. When a pure hydrocarbon is heated in a bomb a complex liquid and gaseous mixture is obtained. The reverse does not occur. Hydrocarbons are known to be unstable at high temperatures and investigation has shown that the rate of decomposition in either the gaseous or liquid phase follows the mono-molecular law. Thus there is no definite temperature at which reaction begins and the rate of decomposition at any temperature can be calculated by the Arrhenius equation. Experiments have shown that when saturated hydrocarbons are heated, unsaturated hydrocarbons are produced and that a fraction of them undergo molecular rearrangements to form saturated cyclic h drocarbons. A further fraction polymerizes or recombines to form complex hydrocarbons of the branched chain or ring type. The transformation of the waxy substances can then be regarded as a sort of low-temperature, high-pressure distillation process in which pressure favors the production of cyclic hydrocarbon. Ultimately, only gases, composed of low molecular weight hydrocarbons, and a dense semi-solid or asphaltic material remain. The maximum depth of oil wells should not greatly exceed 20,000 feet.