Secondary Ion Mass Spectrometry (SIMS) has been used to examine the low-temperature oxidation of coal, using18O2and in conjunction with site-specific reagents in order to identify the surface distribution of oxygen functional groups. This approach leads to some ambiguity in the assignment of functional groups because the inherent complexity of coal chemistry rarely allows any definitive reaction products to be identified. This paper describes results obtained from reaction of coal surfaces with a sequence of reagents designed to remove ambiguous results. This procedure, coupled with SIMS imaging, yields results consistent with an oxidation mechanism which involves the formation of surface peroxides.