Since 2011, production of sweet high gravity oil from the Upper Devonian Berea
Sandstone in northeastern Kentucky has caused the region to become the leading oil producer in
the state. Remarkably, Berea oil is being produced at depths of 2,200 ft or less and in an area in
which the prospective source rocks—the overlying Mississippian Sunbury Shale and underlying
Devonian Shale—are interpreted to be immature for oil production. Further downdip, the Berea
appears to produce primarily gas in the oil window. The economic viability of Berea production
is also a function of reservoir porosity and permeability.