Country System _North America_ Canada Silurian and Devonian Mexico Cretaceous and basal Tertiary Alaska Tertiary (?) _West Indies_ Trinidad Tertiary Cuba Cretaceous and pre-Cretaceous _South America_ Colombia Cretaceous and Tertiary Venezuela Cretaceous and Tertiary Peru Tertiary Argentina Jurassic, Cretaceous and Tertiary _Europe_ Russia Tertiary Roumania Tertiary Galicia Tertiary Italy Tertiary Germany (Alsace) Tertiary and pre-Tertiary _Asia_ India Tertiary Turkestan Tertiary Persia Tertiary _Africa_ Algeria Tertiary Egypt Tertiary _Oceania_ Japan Tertiary Dutch East Indies Tertiary New Zealand Cretaceous and Tertiary From the foregoing table one might conclude that a direct relation exists between the distribution of Tertiary rocks and the supply of petroleum, but in the United States, which produces two-thirds of the world’s current supply, the quest for petroleum has, under scientific direction, included the entire range of the stratigraphic column, and has found petroleum in considerable quantities in the rocks of each geologic system younger than the Cambrian. The fact that seeps and other surface indications of petroleum are generally more pronounced in the relatively younger Mesozoic strata than in the older Paleozoic formations, and the further fact that geologic exploration for oil and gas in countries other than the United States has been restricted in the main to areas containing the most pronounced indications of petroleum, tend to account for the predominance of the Tertiary system in the foregoing table and to indicate the fallacy of attempts to estimate the world’s reserves of petroleum on stratigraphic evidence alone. Despite the broad geologic range of petroleum, its occurrence in specific members, formations, groups, series or systems is by no means universal. On the contrary, its occurrence is restricted to specific localities in which are fulfilled certain variable relations, as yet but little understood, that involve (1) the constitution, sequence and content of organic matter of the sediments; (2) the nature and degree of metamorphism they have undergone; (3) their structure; and (4) their degree of saturation with salt water. Because the most detailed geologic work is insufficient to provide a basis for the appropriate evaluation of the numerous factors involved, and because only a relatively small percentage of the areas of sedimentary rocks in the world have been examined geologically in appreciable detail, any estimate of the future supply of petroleum in the world is peculiarly hazardous. GEOGRAPHICAL DISTRIBUTION