Combustible gases are produced by the radiolysis of bitumen. The evolution rates and compositions of the gases have been determined experimentally. The primary gas evolved is hydrogen. Alpha radiolysis of bitumen, caused by internally incorporated plutonium, evolves more gas than does gamma radiolysis of bitumen. The amount of gas evolved in a given time can be calculated easily by using measured G(gas) values and the contamination level of the bitumen. An estimate of 1.4 for G(gas) is currently reported. The quantity of evolved gas results in some safety considerations on the use of bitumen for the encapsulation of alpha-contaminated wastes.