A process of producing hydrogen by autothermal steam reformation of a hydrocarbon comprises the steps of providing a reactor vessel having a fluidized catalyst bed, introducing steam and a gaseous hydrocarbon, introducing oxygen, maintaining the bed temperature below the spontaneous combustion temperature of the hydrocarbon in a fluidized bed, and withdrawing hydrogen by means of a perm selective membrane. An apparatus for producing hydrogen comprises a reactor vessel, steam and hydrocarbon inlets, an oxygen inlet, a fluidized bed of catalyst within the reactor vessel and a perm selective membrane for withdrawing hydrogen from the reactor.