At least during some part-load operation of a gas turbine wherein a fuel gas is combusted with air with the formation of a flame and the combustion products are let down through a turbine, the fuel gas comprises the product of a stage of catalytic autothermal steam reforming of a light hydrocarbon feedstock gas and the amount of air fed to the gas turbine combuster, relative to the amount of hydrocarbon fed to the catalytic autothermal steam reforming stage, is greater than the maximum amount of air that enables a flame to be sustained in said combustor if that amount of hydrocarbon were to be fed directly to the combustor.