We have used density functional theory with on-site Coulomb interactions (DFT + U) to study the origin of doping effects on the oxygen storage capacity (OSC) of Ce1 - xMxO2 (M = Fe, Ru, Os, Sm, Pu). Substitution of M (M = Fe, Ru, Os, Sm, Pu) in CeO2 results in activated oxygen in Ce1 - xMxO2 compared to pure CeO2 due to its structural and electronic modifications. It is found that the oxygen vacancy formation energy is lowered by doping noble metals. These results are crucial for understanding the doping effects on the OSC of ceria-based materials in heterogeneous catalysis. (C) 2010 Elsevier B.V. All rights reserved.