A method for steam reforming carbonaceous material into a synthesis gas by using a single stage process of heating the carbonaceous material in a rotary kiln at an elevated reforming temperature so that the carbonaceous material undergoes substantially complete conversion to synthesis gas or by using a dual stream, multiple-stage process of heating carbonaceous material to a reforming temperature, below that at which metallic materials will typically vaporize, to form gaseous and solid materials; further reforming the gaseous materials in a second stage reforming kiln at an elevated reforming temperature to form synthesis gas; and separating carbon char from the solid material for further processing.