The following major observations were made in the study. The gas stream from modified in-situ (MIS) retorting of oil shale has a very low heating value, approximately 40 to 60 Btu/SCR. Sulfur appears in the gas primarily as H/sub 2/S, at a concentration of around 700 to 1400 ppMv, dry basis. The primary candidates for control of sulfur emissions from MIS retorting are direct liquid-phase oxidation ot elemental sulfur (the Stretford process), or combustion of the gas followed by flue gas desulfurization (FGD) to remove the sulfur oxides. Selective acid gas removal followed by Claus sulfur recovery does not appear to be a viable sulfur emission control process for MIS retorting, as it may be for some above-ground retorting processes. A better use of liquid acid gas removal solvents appears to be that of non-selective amines to remove both H/sub 2/S and CO/sub 2/ from the gas. The acid gas is sent through a Stretford unit smaller than would be required on the primary gas stream, and upgrades the heating value of the primary gas stream itself, raising the theoretical combustion temperature and reducing ancillary fuel requirements. An overall research plan for environmental aspects of in-situ retorting has been developed and is described in this report. Gas stream controls can be investigated as part of this plan. The specific sulfur control program proposed for OXY's proposed Retorts 7 and 8 at Logan Wash involves installation and testing of skid-mounted units on a slip-stream of retort gas. Units proposed are: (1) Stretford, (2) Incineration with SO/sub 2/ Scrubbing, (3) Non-selective Acid Gas Removal, (4) Molecular Sieves with upgraded particulate removal ahead of the sieves. Including EPA's furnishing of a skid-mounted SO/sub 2/ Scrubbing test unit, the preliminary estimated order-of-magnitude investment for this program is about $1.8 million, versus $3.0 million for a full-flow Stretford unit.