The reduction of oxygen on boron-doped diamond (BDD) and glassy carbon (GC) electrodes was studied in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C2mim][NTf2]. O2 reduction at both electrodes was found to involve the 1e− reduction of oxygen to superoxide. The formation of superoxide was verified by repeating the oxygen reduction on BDD in the presence of benzoic acid, resulting in a shift from the 1e− reduction observed in the absence of benzoic acid to a 2e− reduction yielding the hydroperoxyl anion. The reduction of O2 was found to be quasi-reversible on GC and irreversible on BDD. The significantly slower kinetics observed on the BDD electrode are likely due to the lower electronic density of states in BDD.