Seismic data from the deep Gulf of Mexico basin indicate: 1) inferred ocenaic crust in the deep central Gulf (5 to 6 km thick; 6.8 to 7.1 km/sec.) is flanked symmetrically on the north and south by inferred transitional crust (8 to 15 km thick; 6.4 to 6.8 km/sec.); 2) acoustic basement seen on the reflection data in the central Gulf is an irregular reflector and probably represents the top of an oceanic volcanic (basaltic) layer (layer 2); 3) northof the Campeche Escar pment the top of transitional crust is represented by a strong, smooth reflector/unconformity that truncates rift basins and is onlapped by a thick salt and sedimentary section; 4) in the southeastern Gulf transitional crust consists of tilted basement blocks probably representing a thinned and rifted continental crust; lows between the blocks are filled with synrift sediments; 5) thick salt symmetrically flanks the north and south sides of the oceanic crust; 6) seismic stratigraphic analysis suggests that early sediments in the Gulf in areas of transitional crust represent an upward gradation from volcanics and nonmarine sediments including evaporites to shallow marine and then to deep marine; only deep marine sediments occur in the central Gulf overlying oceanic crust.