It has been established empirically that rapid deposition of sediment with abundant organic matter is required for the formation and accumulation of petroleum. Such conditions may have existed in any part of basins during different periods, therefore the kind of basin and position within the basin may have no close relation to depositional environments of any particular stratigraphic unit. The important thing is to determine for each formation the area which had optimum conditions for the development and preservation of petroleum source material and the deposition of sealed porous strata.

Large deltas which were constructed in rapidly subsiding segments of oceans or large interior sea margins had all the requirements for oil and gas occurrence: plentiful organic remains; rapid deposition which preserved much of the organic matter; relatively slow compaction which allowed the hydrocarbons to escape from the fine-grained sediments and move into the more porous sediment bodies; many porous sands; abundant clay and silt to seal the sands laterally and vertically; and syndepositional development of local "highs." No other environment in the silicate clastic province had all of these favorable conditions.

Petroleum accumulations in carbonate rocks resulted from rapid deposition of organic-rich carbonate sediments in a fast subsiding area with shallow, restricted, marine environments that had periodic influx of fine-grained terrigenous sediments. Porous calcarenites or oolites which formed on shallow, open-sea platforms, or limestone reefs which grew far from shore and were never covered with terrigenous mud, had little organic material preserved to form petroleum.

Numerous undiscovered oil and gas accumulations are in stratigraphic and stratigraphic-structural traps in the favorable facies of terrigenous and carbonate formations. The basins or parts of the basins without the controlling factors should not be explored.

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