The effect of steam on the offgas composition of combustion retorts was determined by interrupting the otherwise continous steam flow in -24 for one hour while other variable, including temperature, remained relatively constant. The offgas composition was determined by frequent gas analyses. zThe largest effect of interrupting the steam flow was to decrease the rate of H2 production by a factor of 2.6 primarily due to to elimination of the H2O char reaction. The rate of CO2 production decreased by a factor of 1.7. After subtracting the CO2 production due to carbon combustion, this result implies that steam accelerates the rate of carbonate decomposition by a factor 3.0. In the aosence of staem, the H2S production rate dropped by a factor of 1.5, indicating the importance of steam-iron sulfide reactions. Finally, the production rate of CO and COS increased by factors of 1.5 and 1.7. these results are compared to results from laboratory studies of oil shale chemistry and to gas production during other parts of this and other LLNL pilot retorts runs. Finally, the ability of steam to significantly decrease the pour pint of shale oil from combustionr etorts is noted.