The Powder River basin of Wyoming offers potentialities for oil and gas accumulations in stratigraphic traps in Upper Cretaceous sands. These potentialities are discussed on a broad basis, at an early stage in development; detailed studies may be undertaken in the future. This paper is confined to the Powder River basin in Wyoming and to the marine section of the Upper Cretaceous and is based primarily on electric-log analysis and correlation.

The Upper Cretaceous section on the east and west flanks of the basin has been known and described since 1911. Oil in the sands has been produced under structurally controlled conditions. Recent discoveries in the Parkman sandstone on the east flank of the basin have focused attention on stratigraphic trap potentialities and active exploration is in progress.

The Upper Cretaceous of the Powder River basin of Wyoming is essentially clastic; shale and sandstone predominate; beds of bentonite, coal, chalky marls, and limestone occur in minor volume. Non-marine Lance and marine Fox Hills formations are not considered in the paper. Typically on the extreme east flank of the basin only one sand zone, the Turner member, occurs in a principally marine shale section. On the southwest flank of the basin numerous sands in the Lewis, Mesaverde, and Frontier formations are present. Pinch-out of these sands on the gently dipping east flank and on anticlinal structures on the west flank of the basin are potential stratigraphic traps.

Maps show areal distribution of 1st, 2d, and 3d Wall Creek, Shannon, Sussex, Parkman, and Teapot sandstones as bars and transgressions of widespread sand beds within marine shale.

Isopachs show structural history of the basin. A "channel" in the vicinity of the Casper arch and positive areas at sites of the Bighorn and Laramie mountains are postulated to account for distribution of various sands.

Asymmetry of the basin and limited areal extent of sands assure potentialities of stratigraphic traps on both the gently dipping east flank and on the highly folded west flank of the basin. Success remains for the future, but a prediction is ventured that major discoveries of oil and gas will be made.