In potentiometric zirconia-based gas sensors, electrodes with medium catalytic activity show a high sensitivity for hydrocarbons (HiCs) when the measurements take place in non-equilibrated oxygen containing gas mixtures at temperatures less than or equal to 800degreesC. This behaviour, explained by mixed potential theory, depends strongly on preparation and particularly on measuring conditions. To learn more about the processes at the electrode surface and their influence on the potential behaviour of the electrodes, we investigated composite electrodes Au-oxide/YSZ with Ga2O3, In2O3 and Nb2O5 as oxides and 80 mass% An and perovskite electrodes made of La1-xSrCr1-yGayO3-delta in N-2-diluted gas mixtures containing O-2 and different combustibles like C3H6, C3H8, CO and C7H8. As compared with perovskite electrodes, gold composite electrodes using Nb2O5 as oxide show enhanced sensitivities especially to C7H8. The temperature dependence of the catalytic activity for the HC combustion correlates very well with the temperature/voltage response. (C) 2003 Published by Elsevier B.V.