A steady state model of moving-bed coal gasification reactors has been developed. Model predictions are in agreement with published commercial plant data for Lurgi pressurized gasification reactors and a pilot plant slagging gasifier. The dependence of reactor performance on operating variables has been studied for Illinois and Wyoming coals. For a given coal, maximum efficiency is determined by the coal-to-oxygen feed ratio. The location of the maximum temperature, which defines the combustion zone, is an important operating variable. Efficient operation of the dry ash reactor cannot be carried out below a critical feed gas temperature because of insufficient gasification and excessive carbon loss in the ash.