The mixed potential response for NO and NO2 from two different oxide electrodes on ytttia-stabilized zirconia (YSZ) was examined at 500 degreesC. The two electrodes were La0.6Sr0.4Fe0.8Co0.2O3 (LSFCO) and Cr2O3. Sensors made with LSFCO electrodes had consistently lower sensitivity towards NOx as compared to those with Cr2O3 and the focus of this paper is to understand the fundamental reasons for the differences in electrode sensitivity. Catalytic activity of the electrodes towards equilibration of NO/NO2 and electrical properties of the electrodes for O-2/O2- chemistry were examined. Based on these studies, it is being concluded that the larger signals for NOx on sensors with Cr2O3 electrodes arise primarily due to the poorer oxygen electroreduction ability of Cr2O3 as compared to LSFCO. (C) 2004 Elsevier B.V. All rights reserved.