The stratigraphic and structural framework of the Gulf of Mexico is described, with particular

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reference to that part with water depths of less than 200 feet, which is considered the limit of economic accessibility for petroleum exploration. This limit encompasses 96,000 square miles bordering the coast of the United States and 56,000 square miles bordering Mexico. Of the total, only the 20,000 square-mile area off the coast of Louisiana has provided economic success.

A cross section from north of Baton Rouge, Louisiana, to Merida, Yucatan, shows the Tertiary Gulf Coast geosyncline. Maps of the Gulf of Mexico are presented showing the extent of the Mesozoic, Early Tertiary, Later Tertiary, and Quaternary sediments that are considered proved or prospective for petroleum within the 200-foot water depth.

The oil and gas development of the continental shelf bordering Louisiana and Texas is described, and a map is presented showing the distribution of the offshore structures that have been drilled or leased to date. As of July 1, 1958, 86 fields had been found by the testing of 123 prospects off Louisiana, and approximately 2.5 billion barrels of oil and 9 trillion cubic feet of gas had been outlined by the successful completion of 1,302 wells out of a total of 1,896 tests. The reserves established by a total of 133 wells drilled off the Texas coast are negligible. While 162 offshore prospects have been tested in the whole area, these represent only about 50 per cent of the structures indicated by geophysical data.

As examples of offshore deep-seated salt-dome fields, structure maps are presented for the Block 110 field, West Cameron area, and the Block 39 (Rollover) field, Vermilion area, Louisiana. A structure map and cross section of the Block 126 field, Eugene Island area, Louisiana, exemplify the shallow piercement salt-dome fields. The occurrence of sulphur on the Block 18 Dome, Grand Isle area, Louisiana, where operations for mining are now under way, is illustrated.

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