The oxygen states on CeO2 surfaces were investigated with DFT + U calculations. The results reveal the variable nature of the oxygen states, including the never before modeled intrinsic peroxide surface defect. Under O-rich conditions, the peroxide defects on the (100) and (110) surfaces is more stable than oxygen vacancies. On surfaces doped with La (III) it is found that under O-rich conditions the (100) and (110) surface will preferentially form peroxide ions in response to the presence of the dopants while the (111) surface prefers oxygen vacancies. Calculated shifts in core levels match experimental binding energies, further suggesting the presence of peroxide species. (C) 2014 Elsevier B.V. All rights reserved.