Experiments were made with a batch reactor to determine the effect of gas pressures, temperature, and gamma radiation intensity on the reaction of CO + cl2 -> cocl2. The equation, dp--de = 0.0110 (1-0.01T) (pcoi) 1/2pc12, where dp--de is the change of pressure of phosgene with time (atm/hr), t is the temperature (deg. C), pco and pc12 are the reactant pressures (atm), and I is the radiation intensity (r/hr), was found to best fit the data. Oxygen and a large ratio of reactor surface to volume retarded the reaction, but inert gases had no effect. A low- temperature reactor system is proposed to take advantage of the conditions which give a high reaction rate with gamma radiation and a simple scheme of product purification.