A 3 electrode, Luggin's Probe configuration was employed in making D. C. polarization and open-circuit potential (OCP) measurements on Platinum and La2CuO4 electrodes in atmospheres containing O 2, NO, NO2, CO and CO2 at 500°C. Each electrode potential, referenced to an isolated embedded reference electrode, changed when exposed to the aforementioned gases and the differences summed to equal the sensor signals previously seen when both electrodes were exposed to the same environment. Both the La2CuO4 and Pt electrode potentials went down when exposed to reducing gases (NO and CO) and went up when exposed to oxidizing gases (O2 and NO2). The Pt responses (AOCP) were larger than those for La2CuO4 for all gases. La2CuO4|YSZ|Pt sensors responded positively to NO and CO, negatively to NO2 and negligibly to O2. The D.C. polarization behavior for the Pt and La2CuO4 electrodes were contrasted and related to their individual gas responses (ΔOCPs). copyright The Electrochemical Society.