The microstructure of the oxide layers formed on both the 9CrODS alloy and NF616 exposed to 600°C supercritical water was characterized using microbeam synchrotron radiation diffraction and fluorescence. This analysis was complemented by SEM observations. Both alloys contain about 9 wt% of chromium and exhibited a three layer structure with an outer layer containing Fe 3O4, an inner layer containing a mixture of Fe 3O4 and FeCr2O4, and an internal oxidation layer containing a mixture of oxide precipitates and metal grains. Nevertheless, the 9CrODS alloy had much thinner oxide layer thicknesses when corroded in the same environment, suggesting improved corrosion resistance due to the influence of the ODS particles. Additionally, one of the NF616 samples was coated with an yttrium layer on its surface prior to oxidation, which enabled the study of such a layer on the corrosion resistance of the alloy in comparison to the presence of ODS particles in the matrix.