Over the last several years our work has focused upon determining the interrelationship between crystallographic and thermodynamic properties of solid state metal oxides and how they relate to achieving simultaneous high ionic and electronic conductivity. This work has led to a new class of oxygen anion and electron conducting brownmillerite derived membrane materials which have been incorporated into catalytic membrane reactors (CMRs) for achieving the spontaneous conversion of natural gas to synthesis gas at practical rates with complete materials stability for extended periods. CMR technology under development at Eltron Research, facilitates the exclusive mediation of oxygen from the atmosphere to a desired reaction site - in this case natural gas partial oxidation to synthesis gas. Because this CMR process is exothermic and eliminates the need for a separate oxygen plant, a significant reduction in synthesis gas production costs may be realized compared co:currently available technology. Additionally, NOx emissions are eliminated since the membrane only mediates oxygen and excludes atmospheric nitrogen. (C) 2000 Elsevier Science B.V. All rights reserved.