Preliminary investigations of pilot-scale oil shale processing plants 1, 2 indicate that the level of mercury in off gasses may be significant. Extrapolation of these results to field conditions suggests that a 100,000 barrel per day oil shale plant processing 100 l/tonne oil shale with an average mercury content of 0.86 ppm 3 may release approximately 32,900 kg of mercury per year to the atmosphere. In contrast, the amount of mercury released from world coal consumption in 1967 is estimated to be 18,900 kg of mercury. 4, 5 These data suggest that mercury emissions from oil shale plants may be of future environmental concern and that they may require control technology to reduce mercury levels. This will require reliable techniques to measure the mercury in these gases.