A solid-state amperometric CH4 sensor using a LaGaO3-based electrolyte was studied. For this sensor, a combination of active (anode) and inactive (cathode) electrodes for CH4 oxidation was applied. Among the various active electrode materials studied, Pd mixed with tin-doped In2O3 (ITO) was found to be the most active electrode and RuO2 the most inactive one. The sensitivities of the sensor using La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) electrolyte to CH4 were approximately 797 mu A/decade at 673 K and 188 mu A/decade at 873 K. The changes in oxygen pumping current upon exposure to CH4 could be attributed to the mixed potential generated by the difference in oxidation activity between the active and inactive electrodes. (C) 2007 Elsevier B.V. All rights reserved.