Oil (bituminous) shale contains organic matter, and when heated yields oil, gas, and other bituminous substances. The commercial distillation of these shales began in Scotland about the time of the Civil War, which was about the time when commercial production from oil wells began in the United States. This industry continues in Scotland and until recent years was carried on in Colorado and Wyoming on a small scale using Green River shales. Bituminous shales are abundant in Kentucky but competition with oil and gas from the usual sources has prevented the development of an oil shale industry to date.

From time to time concern has been felt over the extent of the petroleum reserves of the United States. Although official estimates of the life and extent of these reserves have proved to be too low because of unforeseen discoveries and more efficient recovery, the need for a solution of the problem has been merely deferred.

Distillation tests on Kentucky oil shale (New Albany-Ohio-Chattanooga) by Grouse (1925a) showed an average of 21 gallons (one-half barrel) to the ton and 3,000 to 4,000 cubic feet of fuel gas with net heating value of 337 B.T.U. per cubic foot. The shale oil ran unusually high in motor fuel and gave average amounts of good lubricants.

Kentucky oil shales are a great succession of black shales lying between the Mid-Devonian limestone (or older rocks) below and Waverly (New Providence) above, and they outcrop mainly in the Knobs. In the Knobs north of Irvine the Ohio and Sunbury shales are included. Here the non-bituminous Bedford shale and Berea sandstone intervene and the two shales are readily differentiated. In the southern Knobs, the Cumberland River region of the Pennyroyal, and Pine and Cumberland mountains, it is more commonly referred to as the Chattanooga shale. Around Louisville it is the New Albany shale. Stratigraphic relationships are outlined on page 50. The thickness, as exposed, ranges from 316 feet (combined Ohio and Sunbury) at Vanceburg to 20 to 40 feet in Allen County, 100 feet at Louisville, and in excess of 800 feet in Pine Mountain. The Pennsylvanian also includes some bituminous shales in both the Eastern and Western coal fields, but they are relatively thin and have little promise of value.

Grouse (1925a) estimated that with a tonnage of about 100,000,000,000 available on outcrop, there is available about 50,000,000,000 barrels of crude petroleum, an amount of oil which has never been produced by drilling in Kentucky. Possible by-products of this process have been considered but without much success. These include the spent shale for brick or cement-making and ammonium sulphate (about 37.7 pounds per ton of shale) for fertilizer. Kentucky shales are not so rich as many beds of the Green River shales in the Uinta Mountains of Colorado, which are good for a barrel or more per ton. However, these individually rich layers are interbedded with leaner ones. Kentucky shales have the advantage of proximity to market (population and industry) and an availability for surface stripping.

At present, there is no information available as to variation in petroleum content geographically or stratigraphically.