Non-Nernstian electrochemical gas sensors using yttria-stabilized zirconia (YSZ) as an electrolyte offer a simple and inexpensive way of measuring combustion gas emissions at high temperatures. This work reports the development of potentiometric planar sensors for the specific detection of propene at high temperatures. Nb2O5 and Ta2O5 powders were investigated as sensing electrodes due to their unique catalytic properties toward the decomposition of hydrocarbons. Three Pt vertical bar YSZ vertical bar metal oxide (MOx) planar electrochemical cells were prepared, based on commercial tape-cast YSZ layers, using Nb2O5, Ta2O5, and a Nb2O5:Ta2O5 mixture in 1:1 weight ratio as MOx sensing electrodes, and their sensing performance was compared. All the sensors showed outstanding responses to 1000 ppm of propene in air and propene sensitivities at 700 degrees C, being -214 mV and -190 mV/dec, respectively, the largest for Ta2O5 electrode-based sensors. However, the sensors using the Nb2O5: Ta2O5 mixture electrode showed the best performance in terms of compromising selectivity and stability with keeping large response and sensitivity values. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3486080] All rights reserved.