Geophysicists and exploration geologists who look for oil and gas fields classify the subsurface characteristics, or tectonic setting, of geological structures that contain hydrocarbons.
Any one oil and gas field may reflect influences from multiple geological periods and events, but geoscientists often attempt to characterize a field based on the dominant geological event that influenced the structure's ability to trap and contain oil and gas in recoverable quantities.
A majority of the world's giant oil and gas fields exist in two characteristic tectonic settings—passive margin and rift environments.
[5] Geoscientists theorize that both zones are especially conducive to forming giant oil and gas fields when they are distant from active tectonic areas.
Further analysis shows that giant oil fields typically reach their maximum production before 50% of the ultimate recoverable volume has been extracted.