An entire fixed bed coal gasification reactor is suspended from a large analytical balance for thermogravimetric measurement of the reaction rate. This thermobalance has advantages over the hanging basket types in that sample size can be larger, thermocouples can be embedded directly in the reacting bed, and there is more control over extraparticle mass transfer resistance. Steam gasification of a North Dakota lignitic coal was studied at pressures from 20 to 33 atmospheres and temperatures from 720 to 900/sup 0/C. The observed reaction order was close to one. The gasification rates were essentially independent of the measured temperature. The suggested explanation for this behavior was that the particles act collectively, giving a large resistance to mass and heat transport. The reaction took place under a strong diffusional control. Gas chromatographic analysis of the products indicated that the carbon-steam reaction is the principal gasification mechanism. Steam was in excess, and the products underwent the water-gas shift reaction. Hydrogasification studies were complicated by the observation of an ignition phenomena in the coal bed when the exothermic heat of reaction could not be removed fast enough. An expression for the temperature dependence of the reaction rate was determined. 6 references, 28 figures, 9 tables.