Proper management of large volumes of spent oil shale requires an understanding of the mineralogy and the disposal environment chemistry. Simulated laboratory weathering is one method to rapidly and inexpensively assess the long-term potential for spent oil shales to degrade the environment. The objectives of this study were to assess the solubility relationships of fluorine (F) and molybdenum (Mo) in Green River Formation spent oil shale, to examine the mineralogy and leachate chemistry of three combusted oil shales in a laboratory weathering environment using the humidity cell technique, and to examine the data from spent oil shale literature. Combusted oil shales from the Green River Formation and New Albany Shale were used in the examination of the leachate chemistry and mineralogy.