The Greasy Ridge oil field of southern Ohio is an anomaly because of its accidental discovery and geographic isolation from other oil fields in the Lower–Middle Pennsylvanian Pottsville, New River, and Lee Sandstone play. This study examines its origin within the context of the Devonian shale–middle–upper Paleozoic petroleum system using a robust data set, including geophysical well logs, cores, seismic profiles, and nearby correlative outcrops.

Deposition of the reservoir sand occurred under fluvial and tidal influence in distributary channels of a southwest-prograding, tide-dominated delta. Outcrop analogues reveal northeast, southwest, and bipolar paleocurrents. Reservoir facies occur in the highstand systems tract of a fourth-order (cyclothemic) depositional sequence. Petrographic analysis indicates it consists of fine-grained quartz arenite-sublitharenite, with most porosity formed by mesogenetic dissolution of feldspar and carbonates. Reservoir heterogeneity results from variations in shale content and secondary porosity. The main source rock was the lower Huron Shale Member, which underlies the field. The Betsie Shale formed a seal.

The combination trap resulted from the coincidence of channel sandstone facies with two positive flower structures and structural closure produced by Permian wrench faulting and updip change to impervious, delta plain facies. Seismic profiles indicate two basement faults beneath the flower structures paralleling the Rome trough. The critical moment for generation, migration, and hydrocarbon entrapment occurred during the Early Triassic. These findings differ from earlier studies and should be helpful in discovering and developing other oil fields in Pennsylvanian strata along the basin margin and elsewhere in similar settings.