A favorable diagnosis for oil possibilities is usually made wherever source beds and anticlinal structures occur within sedimentary basins. In many richly petroliferous provinces of the United States these features are not apparent at the surface.

Early Pennsylvanian rocks of eastern Kansas and eastern Oklahoma produce oil from both homoclines and anticlines. Commercial production is limited to a shelf, the margin of which moved northwestward during Atokan and Des Moinesian time. The position of the shelf is discernible at the outcrop.

Shelf sedimentation in the region was littoral to the continental craton, resulting in a lithologic variation in contrast to lithologic uniformity of equivalent strata in the adjoining McAlester basin.

Discontinuity of reservoir rocks and restricted site of oil concentrations are evidence that oil originated, migrated, and accumulated only over the shelf.