Recent results from experiments on the LLL 1/8-and 6-Mg pilot-scale oil-shale retorts have provided new insight into the key oil-loss mechanisms and have suggested a number of practical process-control means for maximizing in situ retort yields. Steam or water mist, total flow, and oxygen flux are valuable process handles in controlling the maximum bed temperatures below 950/sup 0/C. Shale beds containing a broad size range (i.e., 30-cm to 10--m particles) were found to retort with lower yields than beds with smaller particles in narrow size ranges. The lower yield is dominated by the larger shale blocks through coking and cracking within the block and oxidation and cracking of the oil vapor released outside the block. The oxidation loss results from nonuniform flow that lets oxygen penetrate into the retorting zone. Oxidation and cracking outside blocks appeared to be the dominant loss mechanisms. These may possible be controlled by adding steam, water mist, or recycled exhaust gases to the input air. Process control concepts such as stepwise inert-gas injection and thermal-conduction calming are also discussed. Amont the process indicators considered are low-molecular-weight gases, alkene/alkane ratios, and the roughness (i.e., peaks) of the retorting or steam front. 15 figures.