The thermal decomposition of benzoic acid has been studied in a Pyrex reaction vessel at 475, 486, and 499 °C over the pressure range 5 to 40 Torr. The main products, CO2and C6H6, were accompanied by smaller quantities of CO, H2, and biphenyl. The percentage of conversion varied from less than 1% for initial rate experiments to over 90 % in attempts to obtain a material balance. Moderately reproducible initial rates of formation of CO2were obtained after the vessel had been conditioned by pyrolysis of benzoic acid. The order for the initial rate of formation of CO2, 1.20 ± 0.03 at 475 °C and 1.28 ± 0.04 at 499 °C, is discussed in terms of a combination of first and three-halves order reactions. Formation of both C6H5D and C6H6in the presence of C6D5CD3is accepted tentatively as evidence of formation of benzene by both molecular and radical processes.