Formation pressures higher than hydrostatic have been found in all parts of thw world during oil and gas drilling operations. The present paper analyzes the worldwide distribution of these high pressures. Data used include wells from western Europe, Hungary, Poland, Rumania, Russia, the Middle East, the Indian subcontinent, Australia, New Guinea, New Zealand, Japan, the Arctic, the African West Coast, the Red Sea, South America, and the United States. A statistical analysis to define the main geologic characteristics of high-pressure reservoirs was carried out using data from wells penetrating more than 5,000 reservoirs in the Gulf of Mexico, Santa Barbara Channel, and the Anadarko, Permian, and Uinta basins. The probability of finding high pressures in a given depth rang for each of these basins has been established.

The main mechanisms responsible for the creation of these high pressures are concluded to be (1) gravitational compaction, (2) the montmorillonite-illite transformation, (3) wax seals, and (4) tectonic compression. Although in certain instances one of the mechanisms predominates, in most places a combination of them is responsible for the high pressures. Modeling of the geologic processes that have created a basin allows us to recognize in advance the type of pressures to be found there.

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