Abstract We have studied the oxidation of the isomorphic intermetallic compounds UNi 5, UCu 5 and UPt 5 by X-ray photoelectron spectroscopy (XPS). The oxidation of UCu 5 is found to be very rapid, that of UNi 5 moderately rapid, while UPt 5 exhibits resistance to oxidation. The oxide formed is UO 2. Oxidation of UNi 5 and UCu 5 proceeds via diffusion and segregation of U to the surface, while such a process does not occur for UPt 5. Geometrical considerations are used to explain these trends in contrast to earlier suggestions of 5fd bonding effects.