The initial oxidation behaviour of a Ce2O%Ni alloy exposed to air and the longer term oxidation of a metalevaporated magnetic recording tape (MET) of the same composition have been studied using XPS and AES. An Auger depth profile through MET indicated the presence of significant oxygen below the surface oxide, which increased in concentration towards the metal/polymer interfaee. This is explained by penetration of oxygenlwater vapour into both voids and cracks formed during the manufacturing process.