Geocatalytic transformations have been proposed to account for the formation of oil under the mild reaction conditions that prevail in most oil-forming sediments. Several key steps in this process can be rationalized as acid reactions catalyzed by sedimentary minerals. The acid catalytic activity of selected clay and other sedimentary minerals has been determined based on the ability of these materials to mediate the decomposition of tbutylacetate in a low temperature reaction (100°C). For a given clay, the specific acid catalytic activity per gram clay is strongly dependent on the cationic form. For a series of clay minerals saturated with the same cation, the specific acid catalytic activity is proportional to the cation exchange capacity. The specific acid catalyt c activity of a mineral is also proportional to its ability to catalyze such diverse reactions as carbon-carbon bond cleavage, hydrogen disproportionation, epimerization, and decarboxylation. Most petroleum-forming sediments of varying age, origin, and type contain some clay minerals and are found to possess low but measurable acid catalytic activity. These sediments can act as acid active catalysts in the formation and maturation of petroleum.

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