A study was conducted to assess the potential spontaneous combustion hazard of solid waste streams produced in the processing of oil shale. In addition, the utility and precision of various test methods to assess this hazard were determined. The best methods that were found involved a differential scanning calorimetry test and a nonabiabatic oxygen absorption test. In both cases, the sample was slowly heated in air. In the former case exothermic activity was monitored; in the latter, changes in exhaust gas composition were monitored.