We made an experiment on a 30 cm diameter core of Sphagnum-dominated vegetation and peat to estimate the parameters controlling methane oxidation during movement to the ambient air: 13CH4 was added at the water table, and excess 13CO2 appeared in the gas space above the core. At 20¿C in otherwise undisturbed conditions, ~22% of CH4 was oxidized to CO2 during passage up through the overlying 10-cm thick unsaturated peat and plants. We simulated the experiment, with seven parameters: transfer coefficients in water, in the gas phase, and through the container wall; the rate of CH4 and of CO2 generation; and the two parameters of a hyperbolic relation between CH4 concentration and the rate of CH4 oxidation. We optimized these parameters to fit the experimental results, and then were able to generalize to any temperature (0¿--25¿C) and any depth (0--55 cm) of water table. Changing temperature has important effects on the proportion of CH4 oxidized. ¿ 2001 American Geophysical Union