Abstract: A compact, mobile fuel converter for producing molecular hydrogen from hydrocarbon fuels, such as automotive gasoline, or other fuels such as methanol and ethanol has a steam reformer for producing molecular hydrogen from a pressurized and desulfurized fuel and water vapor preheated by flue gases from the fuel processor. The fuel processor is fed with the desulfurized fuel and water mix and a burner is provided to combust off-gas from the fuel processor reaction. Uncombusted off-gas is depressurized and mixed with auxiliary fuel used in the burner. Hydrogen produced in the fuel processor by the steam reforming process is separated from other reformate products using membrane filtration.