In this paper a giant oil field is defined as one containing 500 million barrels or more of recoverable oil; a giant gas field has a minimum of 3.5 Tcf of recoverable gas. At least 187 giant oil fields and 79 giant gas fields are known. Together they contain an estimated, ultimate, minimum recoverable reserve of 638.77 billion bbl of oil and 1,180 Tcf of gas. Reserves of oil remaining to be produced from these giant fields amount to 521 billion bbl.

Of all giant-oil-field reserves, 58 percent is in sandstone and 42 percent is in carbonate reservoirs; 75 percent of giant-gas-field reserves is in sandstone and only 25 percent in carbonate reservoirs. A total of 29 percent of the oil and 10 percent of the gas is in strata of Tertiary age; 63 percent of the oil and 65 percent of the gas is in beds of Mesozoic age; and 8 percent of the oil and 25 percent of the gas is in Paleozoic reservoirs.

The largest number--190 (71 percent)--of the giant fields is in the Eastern Hemisphere; only 76 (29 percent) are in the Western Hemisphere; of those in the Eastern Hemisphere, 154 (58 percent of the world's total) are in a U-shaped belt 6,000 mi (10,000 km) long and 750-1,300 mi (1,250-2,000 km) wide that extends from Algeria to the Arctic Ocean at the longitude of the Polar Urals.