Using both freshly sublimed powders and evaporated thin films, the reactivity of C₆₀ towards molecular oxygen has been demonstrated using the techniques of X-ray diffraction, X-ray absorption, photoemission and infrared spectroscopy. At ambient temperature a molecular intercalation compound is formed, characterised by oxygen-rich surface and sub-surface regions. At higher temperatures oxidation to CO₂ is preceded by the formation of various carbon suboxide intermediates, as reported in the literature.