A systematic comparison of single and binary metal oxide TiO2, TiO2-Ga2O3, TiO2-Er2O3 and TiO2-Ta2O5 gas sensors with nanocrystalline and mesoporous microstructure, prepared by solgel route, was conducted. The gas sensitivity was increased by secondary phase introduction into TiO2 film via two mechanisms, firstly through the inhibition of anatase-to-rutile transformation, since the anatase phase accommodates larger amounts of adsorbed oxygen, and secondly through the retardation of grain growth, since the higher surface area provides more active sites for gas molecule adsorption. The binary metal oxides exhibited a remarkable response towards low concentrations of CO and NO2 gases at low operating temperature of 200°C, resulting in increasing thermal stability of sensing films as well as decreasing their power consumption. The calibration curves revealed that all sensors followed the power law ( B gas A S ] [ = ) (where S is sensor response, coefficients A and B are constants and [gas] is gas concentration). The response magnitude of the sensors obtained in this work is superior to TiO2-based sensors reported in previous studies.