A kinetic study has been carried out on the partial oxidation of methane to formaldehyde over a silica-supported vanadia catalyst. The results indicate that oxygen was adsorbed on the catalyst and took part in the reaction in an Eley-Rideal or Mars-van Krevelen manner. The nature of the interaction with the catalyst was dependent on whether the reaction took place in methane rich (p(CH4) = 80 kPa) or lean (p(CH4) = 4 kPa) conditions. A reaction mechanism for the partial oxidation of methane to formaldehyde is proposed, which is consistent with the data reported here. Methanol oxidation experiments over this catalyst suggested that it was not an intermediate under the conditions employed during this study.