Due to their relatively high sensitivity, improved long-term stability, possibilities for miniaturization and low cost products, mixed potential solid electrolyte sensors can be competitive for the in situ measurement of hydrogen trace concentrations in oxygen containing gases. Their response behavior in non-equilibrated oxygen containing gas mixtures is mainly determined by the catalytic activity of the measuring electrode and depends strongly on preparation and measuring conditions. In this work the sensitivity of electrodes made of composites (Au/MeO) has been investigated in hydrogen containing gases in the concentration range phi(H-2)=0...800 vol.-PPm using a two-chamber setup with Pt-air reference. Electrodes made of Au/Nb2O5 composites show the highest sensitivities of up to 20mV/vol.-ppm at phi(H-2)=10 vol.-ppm and the lowest catalytic activity for hydrogen oxidation. Selected composite materials were tested additionally in self-heated solid electrolyte sensors with both electrodes exposed to the same atmosphere (gas-symmetrical sensor). (c) 2006 Elsevier B.V. All rights reserved.