Full composition of the products of methane air conversion is calculated from the kinetic equations with allowance for the dependence of the methane concentration on the reaction product rate. The derived system of the heat balance equation and kinetic equations of mass conservation provided determination of the maximum yield of hydrogen and carbon monoxide from the total flow rate of methane spent for conversion and retort heating. The maximum yield of the useful product corresponds to the optimal values of the main parameters - temperature at the outlet of the reactor, methane fraction entering the conversion, and minimal fuel consumption. The simulation results match satisfactory experimental data obtained on an EN-60G industrial endothermic generator.