This invention relates to a novel fluidized bed membrane reactor for autothermal operations. More particularly, this invention pertains to a unique fluidized bed membrane reactor which includes internal catalyst solids circulation for conveying heat between a reforming zone and an oxidation zone. A method of producing hydrogen gas from a hydrocarbon gas and steam comprising forming a fluidized bed of a suitable particulate catalyst in a reactor, wherein the catalyst is disposed in the reactor in two reaction modes, the first being an endothermic dehydrogenation reaction mode and the second being an exothermic oxidation or partial oxidation reaction mode, introducing a mixture of steam and hydrocarbon gas into the bottom of the fluidized bed to fluidize the particulate catalyst and form the fluidized bed, reacting the steam and hydrocarbon gas within the first endothermic dehydrogenation reaction mode to produce hydrogen gas, separating said hydrogen gas from other gases in the first endothermic dehydrogenation reaction mode as molecular or atomic hydrogen through a perm-selective membrane that permits the transfer of hydrogen therethrough while preventing or minimizing the transmission therethrough of the other gases in the endothermic dehydrogenation reaction mode, introducing oxidant in the second exothermic oxidation or partial oxidation reaction mode, and mixing same with other gases in the second exothermic oxidation and partial oxidation mode, and directing resultant oxidized gases to the first endothermic dehydrogenation reaction mode.