During the cooling of protective oxide layers on high-temperature alloys, the oxide is usually placed under compression. This paper considers buckling and wedging processes of decohesion of the oxide in this situation. It is shown that the wedging mechanism, in which a tensile wedge crack grows at the oxide-metal interface, is favoured for thick oxides and an intrinsically strong oxide-metal interface. The results of numerical analyses of such wedging failure are presented for the particular case of a chromia film on an austenitic steel. Both elastic and creep deformation processes were considered. It is shown that creep relaxation within the steel markedly reduces the rate of growth of the interfacial crack compared with purely elastic behaviour. Agreement with experimental oxide spallation data is reasonable for this creep case.