Although several geologists have questioned the validity of the carbon-ratio theory, they admit its practical value; the writer, therefore, does not cite evidence of the relation between isocarbs and oil and gas occurrence, but presents the available data indicating that this relationship is produced by tectonic forces more than by conditions of sedimentation. The evidence considered is from the laboratory and the field. The writer concludes that the experimental data regarding the generation of oil and gas from bituminous rocks are at present too meager to furnish any definite evidence regarding the validity of the carbon-ratio theory; that the field evidence indicates that the porosity of sandstones and other reservoir rocks is reduced by dynamic alteration and that thi decrease in pore space is an important factor in causing the absence of oil in areas containing coals of high carbon ratios; that the intense deformation of rocks causes the oil and gas to escape, and that this is one reason why they are absent from areas that have been acted on by great tectonic forces; that the tendency for gas rather than oil to occur in areas of greater alteration is probably due chiefly to the lower porosity of these rocks and to the action of dynamic pressures on the source material, though the variations in the conditions of sedimentation may have been operative also; and that the distribution of marine bituminous strata in the three geosynclines that may be used to test the carbon-ratio theory shows that dynamic alteration and not the conditions of sedimentation is chiefly responsible for the barrenness of the areas in which the carbon ratios of the coals are high.