The selective oxidation of methane to formaldehyde at atmospheric pressure was investigated over a range of silica supported molybdena and vanadia catalysts Promoted with iron, silver, chromium, sodium or cobalt. None of these additives added alone to the silica support assisted in the selective oxidation of methane to formaldehyde, but beneficial effects were observed when molybdenum was subsequently added by impregnation. The vanadium and molybdenum silica systems were compared for a wide range of experimental conditions, including the influence of oxidant ( N2O or O2 ) and the influence of methane content of the feed (methane rich or methane lean conditions). A detailed examination of the influence of vanadia loading on silica was undertaken and this established that vanadia loadings in the range 1-4wt% vanadium gave the best performance.