The invention relates to a method for producing hydrogen gas and optionally a carbonaceous product from a hydrocarbon fuel, comprising: introducing a flowing stream of said fuel into a reaction chamber of a reactor, wherein said reaction chamber has at least one wall and a heating zone which is heated by a heat source, heating said fuel in said heating zone to effect pyrolytic decomposition of said hydrocarbon fuel to produce said hydrogen gas and optionally said carbonaceous product; wherein the ratio of C:O (mol/mol) in the reaction chamber is greater than 20:1; and characterized in that the heat source heats the hydrocarbon fuel in the heating zone by radiated heat to an average temperature of greater than 2000° C. The invention also relates to an apparatus for carrying out the method of the invention.