Tar-sand deposits in western Kentucky have been recognized as a potentially significant mineral resource since the middle of the 19th century. Deposits of bitumen-bearing Late Mississippian and Early Pennsylvanian sandstones have been reported both at the surface and in the subsurface for a distance of approximately 100 miles along the southeastern rim of the Eastern Interior Basin.
Prior to 1981, published studies of western Kentucky tar-sand deposits had concentrated on the outcrop areas where bitumen-bearing sandstones were present at or near the surface. In-place oil resources were estimated at less than 50 million barrels (MMbbl). Reports that delineated subsurface occurrences of asphaltic sandstones in western Kentucky were not available.
In 1981 the Kentucky Geological Survey initiated a project to inventory and evaluate the oil-resource potential of the asphaltic sandstones in the subsurface of western Kentucky. A preliminary report on the Big Clifty (Late Mississippian) was published in 1982.
In 1982 this project was combined with the Interstate Oil Compact Commission's (IOCC) project to catalog and evaluate the tar-sand-resource potential of the United States. Results of investigations by the Kentucky Geological Survey, in conjunction with Lewin and Associates, who were selected to compile the IOCC report, have confirmed that major tar-sand resources are present in western Kentucky. In-place resources are calculated to be in excess of 3 billion barrels (Bbbl).