Synergetic depositional and deformational phenomena have resulted in large concentrations of oil and gas in the upper Miocene and Pliocene sections of the Gulf Coast geosyncline. Most of these accumulations have been found trapped in the sandstone and sandstone-shale magnafacies. The gulfward limit of future exploitation can be determined reasonably from present data, and should extend to water depths of 600 ft (180 m). Any significant future discoveries are most likely to be in the offshore. Development of these facies in Louisiana is approaching maturity, but there should be limited extensions gulfward and eastward of present production. Offshore Texas is largely unexplored, but results of drilling have been disappointing.

Exploration for turbidites in the shale magnafacies gulfward of present trends is a challenge both to explorationists and to management. Turbidites will be difficult to locate and drilling will be expensive. They must be thick and prolific reservoirs in order to be commercial--but it is possible that such thick sequences are present.

A possible future source exists in the shale magnafacies where turbidite sandstone reasonably can be expected on the updip flanks of salt structures and in the lows between them. The search for reservoirs of this type, particularly in the younger sections, will involve operations beyond the continental shelf in water depths that increase abruptly from 600-ft (180 m) depth. Exploration in the older beds will require increasingly deeper drilling. Exploration for turbidites requires complex seismic techniques and the best efforts of geologists, paleontologists, and geophysicists. No realistic estimate of favorable sedimentary-rock volume in the shale magnafacies is possible at this time.

Present economics barely have justified the oil industry's exploration of the sandstone and sandstone-shale magnafacies in water less than 600 ft deep. Thus, more costly exploration in the deeper waters beyond the continental shelf will depend on increased incentives. Otherwise, economic considerations may jeopardize all future exploration in the Gulf of Mexico.