The formation of different gases in the thermal decomposition of cellulose and pine sawdust has been studied. The kinetic constants of CO2 and H-2 formation in cellulose decomposition have been determined from results obtained in isothermal experiments. These kinetic constants have been taken as representative of pine sawdust decomposition at T > 292 degrees C, and values for lower temperatures have been obtained from isothermal experiments performed with pine sawdust. For both materials, a simple model without adjustable parameters has been applied that allows us to calculate the local temperature, solid conversion, and yield of each gas. The results obtained in dynamic experiments with heating rates ranging between 2 and 53 degrees C/min have been compared with the theoretical results, and an acceptable agreement has been achieved.