The selective oxidation of methane in aqueous hydrogen peroxide over ZSM-5 catalysts with different Si/Al ratios has been investigated. Methyl hydroperoxide was confirmed as the initial product of methane oxidation by a study of product distribution versus reaction time in agreement with previous work. Formaldehyde was identified as an intermediate in the oxidation reaction pathway from MeOOH to formic acid and ultimately CO2. Hydrogen evolution during the oxidation of methane is reported for the first time. Oxidation of the HCHO intermediate to formic acid was demonstrated to be the source of the evolved hydrogen. HCHO appeared to be the source of low levels of soluble polyoxomethylene. Higher productivity of liquid oxygenated products is reported compared to previous work.