Hydrogen permeation in 30% Mo-substituted lanthanum tungsten oxide membranes, La27Mo1.5W3.5O5.55 (LWMo), has been measured as a function of temperature, hydrogen partial pressure gradient, and water vapor pressure in the sweep gas. Transport of hydrogen by means of ambipolar proton-electron conductivity and -with wet sweep gas -water splitting contributes to the measured hydrogen content in the permeate. At 700 degrees C under dry sweep conditions, the H-2 permeability in LWMo was 6 x 10(-4) mL min(-1) cm(-1,) which is significantly higher than that for state-of-the-art SrCeO3-basect membranes. Proton conductivity was identified as rate limiting for ambipolar bulk transport across the membrane. On these bases it is evident that Mo-substitution is a successful doping strategy to increase the n-type conductivity and H-2 permeability compared to nominally unsubstituted lanthanum tungsten oxide. A steady-state model based on the Wagner transport theory with partial conductivities as input parameters predicted H-2 permeabilities in good agreement with the measured data. LWMo is a highly competitive mixed proton-electron conducting oxide for hydrogen transport membrane applications provided that long term stability can be ensured. (c) 2014 Elsevier B.V. All rights reserved