Following an in situ retorting experiment in Green River oil shale near Rock Springs, Wyoming, at a depth of 70-88 ft, the U.S. Bureau of Mines conducted a second experiment on a larger scale and at a greater depth (110-145 ft). Combustion was initiated after explosive fracturing, but the rate of combustion attained was insufficient, and an hydraulic fracturing treatment was tried in an attempt to increase the surface available for combustion; however, combustion of shale continued to be limited by the availability of fuel. Pattern for injection, production, and monitoring wells, the fracturing procedures, and the measures taken to evaluate results are described.