Samples of Illinois shales and a limestone containing organic materials were tested to determine their oil content and to evaluate their possibilities as sources of oil. Oil content of the Pennsylvanian shale samples ranged from 0 to 40 gallons per ton, but only 3 samples contained more than 25 gallons per ton, whereas 88 percent contained less than 15 gallons. Of the shale formations for which 3 or more samples were tested, that above coal No. 2 in northern and western Illinois contained the highest average oil content, almost 16 gallons per ton.