Oxidation of butan-2-one (methyl ethyl ketone) to diacetyl has been studied by passing the former over vanadium oxide and vanadium phosphorus oxide catalysts in the absence of gas phase oxygen, until the oxygen donation capacities of the solids were exhausted. Improved selectivities to diacetyl were observed when comparison was made with operation in the presence of gas-phase oxygen; reaction rates were similar. The spent oxides were readily regenerated by treatment in air. Operation in anaerobic conditions led to lower levels of C-C scission products and in particular eliminated the pathway whereby the enol form of methyl ethyl ketone reacts with adsorbed molecular oxygen to form acetic acid and acetaldehyde, which represents the major non-selective route in methyl ethyl ketone oxidation to diacetyl in aerobic conditions.