Mixed potential solid electrolyte sensors are suited for the in situ measurement of hydrocarbons (HCs) in exhausts with respect to their potential for long-term stability, miniaturization and low-cost solutions. Their response behavior in nonequilibrated oxygen containing gas mixtures is mainly determined by the catalytic activity of the measuring electrode and depends strongly oil preparation and measuring conditions. In this work, the sensitivity of electrodes made of perovskites (La1-xSrxCr1-yGayO3-delta) and composites (Au/MeO) was investigated in different combustibles including CO, C3H6/8, C7H8, and CH4. Gas symmetrical mixed potential sensors were produced and characterized with electrodes made of Au/Nb2O5 composites, which show maximum sensitivity. By using platinum (Pt)-reference electrodes without equilibrium behavior, the sensors are applicable in lean and rich mixtures as well. (C) 2004 Elsevier B.V. All rights reserved.