Sixty-three orogenically controlled oil and gas fields have been discovered in the Zagros sector of southwest Iran since the turn of the present century. Most of the fields are giant, multi-reservoir accumulations producing from fractured carbonate pay zones ranging in age from Permo-Triassic to Oligo-Miocene.
The most prolific oil-producing zones are the Asmari Formation (Oligo-Miocene) and the Bangestan Group (Upper Cretaceous). The available geochemical evidence indicates that the major source of the oil is the underlying Lower Cretaceous (Albian) Kazhdumi Formation.
It is argued that, in the main oil-producing area, the Kazhdumi source rock was not buried to the depth required for hydrocarbon generation until the Eocene, and that no significant oil expulsion took place until the Miocene. Entry of oil into the reservoirs is geologically a recent event; it postdates the late Miocene-Holocene Zagros orogeny that resulted in the formation of the present structural traps.
It is suggested that the development of growth structures during the Late Cretaceous and Paleogene could have contributed to some hydrocarbon localization prior to the formation of the late Tertiary traps.