We have performed extensive research on the development of new types of solid state combustion gas sensors over the last decade. The combination of new electrode materials, insights from sensor studies equipped with auxiliary reference electrodes, heterogeneous catalysis measurements and theoretical analysis has enabled the development of novel gas sensors at the Los Alamos National Laboratory. The substitution of electronic conducting oxides for Pt electrodes has extended the applications of Nernstian-type zirconia oxygen sensors to high temperatures >900 degreesC and high sulfur environments. Novel sensor geometries that allow for gas diffusion through a porous electrolyte to a dense electrode improve the performance of mixed potential type sensors. We have also developed porous electrolyte potentiometric sensors that detect non-methane hydrocarbon gases in exhaust streams. (C) 2004 Elsevier B.V. All rights reserved.