An ab initio study of the adsorption of NOx and SO2 onto SnO2(110) surfaces is presented and related to gas-sensing applications. Using first-principles calculations density functional theory-generalized gradient approximation (DFT-GGA), the most relevant NO and NO2 adsorptions were analyzed by estimating their adsorption energies. The resulting values were compared to experimental desorption temperatures for NO and NO2. The adsorption of the poisoning agent SO2 was also analyzed. Optimum SnO2 working temperatures for minimum SO2 poisoning in NO2 sensing applications are discussed from the perspective of adsorption. In all cases, we observed that the surface reduction state has dramatic consequences on adsorption strength. An ab initio thermodynamics study is presented to analyze the stability of several surface oxygen configurations with respect to the ambient oxygen partial pressure and the temperature of the material. (c) 2007 The Electrochemical Society.