West Bastian Bay field, one of the largest gas fields in the south Louisiana Gulf Coast area, produces from beds of late Miocene age between 6,950 and 15,500 ft. Structurally, the field is an anticline on the southern downthrown side of a fault whose throw exceeds 3,000 ft. The center of uplift moved progressively northwestward for a distance of 2 mi. from its "X" Sand position near the southeastern edge of the field. The fairly recent development of a new locus of uplift near the eastern edge of the field has given the field a double closure at the level of the uppermost Miocene beds. A small, long-quiescent fault with 60-100 ft. of throw across the axis of the fold and the eastern part of an axial fault separate the deep reservoirs in the northeastern segment of the fie d from the deep reservoirs in the other segments. The fact that gas columns in this area are thinner than elsewhere along the apex of the fold is believed to be the result of the presence of the nearby East Bastian Bay field and the eastward shaling out of the "W" and "X" Sands.

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