The partial oxidation of methane to synthesis gas has been studied in the heat integrated wall reactor (HIWAR). The reactor comprises a ceramic tube on the inner and outer surface of which a metal catalyst film is deposited in the form of a washcoat. The combustion reaction is taking place on the inner catalyst film and the reforming reaction on the outer, absorbing simultaneously the heat of combustion. Thus, the heat integrated wall reactor offers the possibility of reducing the magnitude of hot spots which normally develop during the exothermic combustion of methane in conventional reactors, due to rapid heat transport across the tube wall from the combustion to the reforming zones. The HIWAR can be operated in the adiabatic mode.