The stratigraphic and structural framework of the Gulf of Mexico is described, with particular reference to that part of the continental shelf 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 the coast of Mexico. Of this total area, only the 20,000 square-mile area off the coast of Louisiana has provided economic success as the result of offshore exploration. Approximately 2.5 billion barrels of oil and 9.5 trillion cubic feet of gas had been outlined by the drilling of 2,019 offshore wells to July 1, 1958. Though 162 offshore prospects have been tested, these represent only about 5 per cent of the structures indicated by geophysical data.

Maps of the Gulf of Mexico are presented showing the extent of the Quaternary, Late Tertiary, Early Tertiary and Mesozoic sediments that are considered proved or prospective for petroleum exploration on the continental shelf within the 200-foot water depth limit.

As examples of typical offshore salt-dome fields, structure maps and cross sections are presented for the Block 126 field, Eugene Island area and the Block 110 field, West Cameron area, Louisiana. As an example of the magnitude of associated salt intrusions, a structure map of the Marchand-Timbalier-Caillou Island salt massif is given. This salt massif contains 265 cubic miles of salt down to the mapped depth of 20,000 feet, and assuming the salt extends downward with vertical sides from that depth to a depth of 50,000 feet, an estimated 1,400 cubic miles of salt are present.

The occurrence of the sulphur deposit on Block 18 dome, Grand Isle area, Louisiana, where the Freeport Sulphur Company is beginning mining operations, is illustrated.

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