A reactor comprising: a hollow shell defining a hermetic enclosure; a plurality of tube sheets disposed within said hermetic enclosure, a first one of said plurality of tube sheets defining a first chamber; at least one reaction tube each having a first end and an opposing second end, said first end being fixedly attached and substantially hermetically sealed to one end of said plurality of tube sheets and opening into said first chamber, the second end being axially unrestrained; each of said reaction tubes is comprised of an oxygen selective ion transport membrane with an anode side wherein said oxygen selective ion transport membrane is formed from a mixed conductor metal oxide that is effective for the transport of elemental oxygen at elevated temperatures and at least a portion of said first and second heat transfer sections are formed of metal; each of said reaction tubes includes first and second heat transfer sections and a reaction section, said reaction section disposed between said first and second heat transfer sections; a reforming catalyst disposed about said anode side of said oxygen selective ion transport membrane; a first process gas inlet; a second process gas inlet; and, a plurality of outlets.