The Delaware basin is a strongly negative structural depression in western Texas and southeastern New Mexico. The early history of the basin was part of that of the western mid-Paleozoic Tobosa basin (Fig. 1). Its history as a separate basin began with the rise of an Early Pennsylvanian median ridge in the Tobosa basin. During the Pennsylvanian and Permian 20,000 feet of sediments accumulated in the deep Delaware basin trough. These basinal sediments consist largely of clastics in contrast to the thinner equivalent carbonate sections deposited on the surrounding shallow shelves. Water depth was a controlling factor in this facies distribution pattern. Clastic supplies were limited and throughout its history waters in the Delaware basin were deep. Only near the end of the ermian, when the basin filled with evaporites, did the surface of sedimentation reach sea-level. Formation of a late Paleozoic geosyncline, which includes the Delaware basin, was associated with high-angle faulting rather than crustal folding. Exploration has not proceeded far enough to justify discussion of local structures within the Delaware basin.