It has been shown that the pyrolysis of cellulose at low pressure (1.5 Torr) can be described by a three reaction model. In this model, it is assumed that an "initiation reaction" leads to formation of an "active cellulose" which subsequently decomposes by two competitive first-order reactions, one yielding volatiles and the other char and a gaseous fraction. Over the temperature range of 259–341°C, the rate constants of these reactions, ki (for cellulose → "active cellulose"), kv (for "active cellulose" → "volatiles"), and kc (for "active cellulose" → char + the gaseous fraction) are given by ki = 1.7 × 1021e− (58,000/RT) min −1, kv = 1.9 × 1016e− (47,300/RT) min−1, and kc = 7.9 × 1011e− (36,600/RT) min−1, respectively.