Of the 135 countries of the world whose current status of petroleum exploration was reviewed, 65 are producing oil and gas (including 2 about to have production); in 70 countries activity is confined to exploration or preparations to explore. About 90% of the petroleum exports from the noncommunist world flows from Arab or closely affiliated countries.

At least 75% of the world's proved and potential petroleum reserves exist beneath the continental terrace, which includes the coastal plain, the continental shelf and slope, and also many partly enclosed seas, gulfs, bays, deltas, estuaries, straits, etc.

Most of the available basins of the world, as well as some nonbasin areas, including the offshore shelves, etc., have been leased for petroleum. There is a wide tendency in area selection to overvalue the less attractive and commercially submarginal areas, and to underestimate the potential of the much smaller percentage of bonanza class areas. The greater part of the leased area of the world is of the former type.

World production has more than doubled in each of the last 2 decades to 48 million bbl/day in 1970. If production merely doubles in each of the next 2 decades a minimum of 22 trillion bbl of new oil must be added to meet the production demands of the period and leave a 20-year supply ratio (15 trillion bbl to leave a 10-year supply ratio). The current year's supply ratio is 31; also 15 to possibly 25 trillion bbl of oil is the range of estimates by informed geologists of recoverable liquid oil (proved plus potential) remaining in the world. By any reasonable projection, the years of the petroleum age are finite.

The demand for petroleum energy has been growing at a rate 3 to 5 times the rate of population increase, and over the present decade will more than equal that of the 112 prior years following Col. Drake's discovery. The rate of finding giant and supergiant fields does (or soon will do) no more than keep pace, and then only briefly, with the years supply ratio. The time required to find and develop the main crop of fields in new producing basins has very rapidly and greatly decreased. Some geologists have looked unduly to the stratigraphic trap, greater depths of drilling, and the deeper ocean bottom areas as the answers in meeting the petroleum demands of the future.

Worldwide oil occurrence studies indicate that the temperature gradient varies greatly over the world's basin areas, and from basin to basin, depending on the geologic background. They also indicate that the gradients have a strong influence both on the incidence of petroleum occurrence and on the initial and optimum depths of such occurrence. This apparently explains in a large and often critical measure many of the unanticipated exploration disappointments as well as successes.

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