"Successful startup of an in situ retorting experiment in the Tipton Member of the Green River oil shale formation near Rock Springs, Wyoming., began on April 5, 1976, at Rock Springs site 9. The target shale was located in a 40-foot zone between 137 and 177 feet beneath the surface and averaged 21 .3 gallons of oil per ton and 2.3 percent water by Fischer assay. After fracturing the shale zone with a combination of hydraulic and explosive fracturing treatments, the oil shale was ignited at a central air injection well with a electric heater and a propane burner. The oil shale was retorted in advance of the combustion front which propagated radially toward eight surrounding production wells. About 700 gallons of oil and 165 MM Btu of low-Btu gas were recovered during the first 35 days of operation. Preliminary evaluation indicates that only a fraction of the oil shale reserves were retorted in advance of the combustion front. A computer data acquisition system automatically monitored underground temperatures, pressures, gas flow rates, and gas compositions at hourly intervals. Based on integration of these measurements, energy and material balance calculations indicate that the maximum amount of shale retorted in specially designated test areas was probably less than 14 to 18 percent of the oil shale reserves within the 40-foot zone. Post- retorting core samples will be evaluated after the experiment is finished. At the time this paper was prepared, the experiment was still continuing and data from only the first 35 1/2 days of operation were available. When the experiment is completed, data from environmental monitoring of the experiment will also be evaluated to determine the impact of in situ oil shale processing on air, water, and land quality."