The interactions of gas phase oxygen with gadolinia-doped ceria (GDC) surfaces are investigated by electron stimulated desorption (ESD). The primary desorbed cationic species related to molecular oxygen adsorption is O-2(+). The threshold energy for ESD of O-2(+) is 13-14 eV, indicating electron impact ionization of molecular oxygen bound at oxygen vacancies. Dependence of O-2(+) velocities upon incident electron energy and substrate temperature reveals the dominant influence of the effective charge of the adsorption complex. The O-2(+) velocity distribution is bimodal, and the onset of the faster components at room temperature is related to the balance between fluxes of incident electrons and secondary electron emission, causing effective hole production and neutralization of trapped electrons at surface states. (C) 2008 Elsevier B.V. All rights reserved.