The Cincinnati arch is a low, broad, anticlinal fold approximately 700 miles long and 250 miles wide on which many local folds are found. The axis extends from northern Ohio and Indiana into northeastern Mississippi, and passes through central Kentucky and Tennessee. The rocks involved are chiefly limestones which range in age from Cambro-Ordovician to Lower Pennsylvanian.

Natural gas occurs on minor folds on the flanks of the arch, in lenticular reservoirs off local structures, as up-dip accumulations in reservoirs of differential porosity and up-dip terminations of reservoir rocks against unconformities. Commercial gas fields have been developed on the arch in Kentucky, Tennessee, Mississippi, and Alabama. The gas is found chiefly in porous or fissured limestones of Mississippian, Devonian, Silurian, and Ordovician age, and in sandstones of the Chester series of Mississippian age.

This paper is a brief survey of the stratigraphic and structural conditions which influence the occurrence and production of natural gas in the southern part of the Cincinnati Arch region.