In this investigation, the oxide growth mechanisms of a Pt–aluminide type coating were investigated using a two-stage oxidation treatment. The samples are first oxidised in unlabelled 16 O 2 , followed by a second oxidation in 18 O 2 enriched tracer gas. Oxygen diffusion characteristics through the oxide scale were determined by SIMS depth profiling. Focused ion beam analysis was also conducted using a Ga + ion beam to mill cross-sections and then perform elemental mapping. Encouraging results have been obtained from this series of experiments and have clearly shown the two different oxidation mechanisms that occur at temperatures above and below approximately 1000 °C which are associated with the formation of θ and α alumina scales.