CeNbO4+delta has been shown to undergo reversible redox processes as a function of both temperature and time. However the associated phase transitions are not fully reversible and this unusual feature is reflected in spectra obtained from near edge X-ray absorption spectroscopy of the Ce L-III edge. Two materials have been studied: CeNbO4.08 and CeNbO4.25 and it is found that the oxidation and reduction rates for these two materials differ significantly and that the thermal history of the material dramatically affects the extent and rate of redox activity. (C) 2009 Elsevier B.V. All rights reserved.