At present, there are 509 known giant oil and gas fields in the world. A giant is defined as having 500 million barrels of recoverable oil or equivalent gas. Less than one-third of this discovered amount has been produced to date; thus, remaining reserves are sufficient, at present production rates, to last well into the 21st century.

Geologically, the giants are found most commonly in provinces that can be classified as having formed in continental crust and having been associated with a plate collision. Basins in these provinces are found across a wide range of geographic areas, many of which remain only moderately or lightly explored. The basins offer, therefore, significant geologic scope for future exploration.

The discovery rate of giant fields has decreased since the late 1960s, indicating that the Hubbert cycle of oil resource exploitation is in a mature phase. Given the basins yet to be explored, this decrease is due to economic, rather than geologic, factors.

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