When Hg losses to the retort were minimized, 80 to 100% of the Hg originally present in the raw shale partitioned to the untreated offgas. Seven percent or less of the Hg partitioned to the oil. Approximately 2% of the Hg remained in the processed shale which had been heated to 500/sup 0/C in N/sub 2/. Distribution to the water was negligible. Gaseous Hg evolved from the shale as a single pulse over a temperature range of 160 to 320/sup 0/C. The laboratory and simulated in-situ retorting experiments suggest that adsorption of Hg on unretorted or partially retorted shale ultimately controls the movement and final release of Hg to the offgas during MIS retorting. The laboratory experiments also demonstrated that adsorption and condensation losses of gaseous Hg to the retorting system can be substantial. Invoking a number of assumptions it was possible to estimate atmospheric Hg emissions for underground retorting at a MIS oil shale facility producing 8 x 10/sup 6/ liters (50,000 barrels) of oil per day. Hg emissions from a MIS facility could exceed emissions limitations which have been established for other industries. It is possible that retort design parameters and retort operating procedures can be used to control Hg emissions from MIS retorting.