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Abstract: The oxygen vacancy formation on the CeO2(110) surface has been studied by ab initio electronic structure calculations. Embedded-cluster calculations with explicit treatment of the electron correlation from Møller–Plesset perturbation theory (MP2) provide an alternative description of the surface O vacancy compared to previously reported periodic density functional theory (DFT) calculations. The electronic structure at the MP2 level shows a complete localization of the excess electrons on the two surface Ce ions neighboring the vacancy, contrary to the delocalized description seen in the periodic DFT calculations for the CeO2(110) surface (but more in line with DFT+U results recently reported for the partially reduced CeO2 bulk and (001)-surface). Our calculations predict a vacancy formation energy (3.1–3.3eV at the MP2 level including basis set superposition error (BSSE) correction) and a geometric structure in qualitative agreement with the periodic DFT results, where the surface O ion next to the vacancy assumes a bridging position between the reduced Ce ions. [Copyright &y& Elsevier]