Recently, a detailed statistical study was made of 236 or all the free world's major oil fields (those with 100,000,000 barrels or more ultimate recovery). These fields account for 217 billion barrels or 82.5 per cent of the ultimate reserves discovered to date outside the Soviet orbit. According to the results obtained, the bulk of the oil occurs: (1) on the stable side of basins, (2) in anticlines, (3) in sandstone and carbonate reservoirs, (4) from formations of Mesozoic age or younger, (5) from a depth range of 2,000 to 8,000 feet.

Most of the discovered free world ultimate oil is 30° API gravity or lighter, with mixed asphaltic-base oils predominating. Both the number of fields and the volume of reserves have been cyclic with ten-year intervals starting in 1917.

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