Surface properties of solids and the interactions between molecules and solid surfaces are important for many technical applications. They also involve a range of physical and chemical phenomena of fundamental scientific interest. The importance of oxygen chemistry at SnO2 surfaces follows from the fact that SnO2 is used as an active material in gas sensor applications. The operation principle of these sensors is usually based on measurable conductance response of the material, which is understood in terms of reactions of gas molecules with different oxygen species adsorbed onto the surface. The role of the lattice oxygen, but in particular, the bridging oxygen atoms on SnO2 surfaces, is also active. Detailed understanding of the reaction mechanisms of various oxygen species at SnO2 surfaces is important, as it offers a way to improve the sensitivity and selectivity of the sensors. Oxygen adsorption-desorption kinetics at the SnO2 surface is studied experimentally using O-2-temperature-programmed desorption (TPD) method together with conductance measurements in the case of SnO2 powder and polycrystalline thick films made from the powder. In addition, CO-TPD is studied and the transient behaviour of various oxygen species is considered. Molecular beam epitaxy (MBE) was also used to fabricate polycrystalline and monocrystalline thin films with the SnO2(101) face on single crystal sapphire substrate. Simultaneous surface potential and conductance measurements during heating and cooling in different ambient atmospheres were used to characterize the monocrystalline SnO2(101) surface after various surface treatments. (c) 2005 Elsevier B.V. All rights reserved.