The nature of the surface complexes formed when graphite is exposed to thermal or reactor-irradiated CO2 or O2, and their role in carbon gasification, have been deduced by temperature programmed desorption to 1075 K. A series of complexes with discrete activation energies of desorption (21–274 kJ mol–1) which desorb by first-order processes have been observed. They are attributed to adsorption at carbon atoms on the graphite surface adjacent to edges and vacancies. The site responsible for radiolytic oxidation of graphite by CO2 has been tentatively identified from the variation in surface coverage and desorption energies in the presence of radiation or on addition of CO or CH4 to the CO2.