Experiments designed to simulate various modified in situ (MIS) retorting conditions are being carried out in large (6-t) and small (150-kg) pilot retorts at Lawrence Livermore National Laboratory (LLNL). Both retorts are operated under near adiabatic conditions by a system of computer-controlled sidewall heaters. Access ports positioned every 15 cm down the length of the retorts provide locations for inserting thermocouples and gas probes into the rubble bed. All data acquisition and real-time analysis are presently carried out via a dedicated Hewlett-Packard 1000 computer system. To date, 25 experiments have been conducted using these retorts. The results from these experiments are summarized in a set of process correlations showing the effects of: inlet gas composition; particle size; grade; grade changes; and retorting rate. From these data, it is possible to estimate the results from a particular field MIS retorting experiment operating under a given set of conditions. In several instances, results from the LLNL mathematical retort model are used to extend and explain the results of the experiments. Recently, we have also used the retorting model as a process control tool for establishing the proper operating conditions prior to the burn. The results of the preburn calculations are found to be in good agreement with the actual pilot retorting data.