The reactivity of a C,, + 15% C,, fullerene mixture in various gases was studied using thermal analysis (TG/DTA) and infrared spectroscopic techniques. The thermal behavior of fullerenes was found to be complex and strongly dependent on the heating rate, overlapping of different phenomena taking place. Comparison with the behavior of a number of carbon materials showed that the reactivity of fullerenes in air is similar to that of the least ordered forms of carbon. An interesting feature is the appearance of various exothermal O2 gasification peaks as the heating rate is increased. C, undergoes concurrent sublimation and partial decomposition during heat treatment, leaving carbonaceous residues which are partially or totally gasified depending on the reactivity of the surrounding atmosphere. Condensed solids from the sublimation process could be recovered on the cool parts of the thermobalance; mixtures richer in C, than the starting one were obtained in Ar whereas heating in COa led to recovery of oxygenated fullerene derivatives. Carbonaceous residues from pyrolysis in Ar and CO2 were strong infrared absorbers and contained oxygenated (epoxy and carbonyl) functional groups.