The oxidation kinetics of methane in supercritical water were determined in an isothermal, plug flow reactor over the temperature range 560-650 °C at 245.8 bar. The oxidation rate was found to be first order in methane concentration and [formula omited]-order in oxygen concentration. The activation energy over the temperature range 560-650 °C was 42.8 ± 4.3 kcal/mol. A pressure-corrected elementary reaction model for gas-phase combustion was applied to the oxidation of methane in supercritical water. Reaction path analysis identified several key reactions but the model underpredicted the methane conversion by a factor of 5 and predicted a first-order activation energy of 66 kcal/mol over the temperature range 560-650 °C. Variation of the rate constants for a few important reactions within their uncertainty limits resulted in reasonable agreement with experimental data. A more detailed examination of elementary reactions in supercritical water is therefore warranted.