Oxygen intercalation into a pyrochlore at room temperature is reported. A simple chemical route was employed. Previously only perovskite or a few closely related phase have demonstrated an ability to act as hosts for such intercalation. The specific system studied was the interstitial solid solution Ce2Zr2O7+x (0 less than or equal to x less than or equal to 0.36). Neutron diffraction reveals that interstitial oxygen enters the tetrahedral 8b sites (space group ), which are empty in stoichiometric pyrochlore, but displacement of existing oxygen from the tetrahedral 8a sites also occurs. The lattice contracts on intercalation due to oxidation of Ce3+. The changes in structure and the diffusion pathways for oxygen are discussed.