The standard energy of combustion of fullerene soot generated in are discharge was determined to be -36.0 +/- 0.5 kJ g(-1) by oxygen-bomb combustion calorimetry. The value was much closer to those of C-60 and C-70 than that of graphite. This result provides an energetic reason for the remarkable yield of fullerenes in are discharge and supports the mechanism of fullerene formation, where fullerenes are the lowest energy products. Fullerene onion formation is interpreted in terms of energy relaxation of the fullerene soot.