It is well documented that the adherence of protective oxide scales to alloy substrates is significantly improved by small alloy additions of such less-common elements as yttrium. This important effect is little understood, however. The lack of structural data is believed to be the major reason for this lack of understanding. Accordingly, we are determining the oxide scale and substrate morphologies of model oxidation resistant alloys. In what follows, we present and discuss the structural details of the nonadherent Al2O3 scale on Fe-25Cr-4Al (wt pct) and the adherent Al2O3 scale on the same alloy with about 0.1 wt pet yttrium or scandium.The Al2O3 scales are developed by oxidizing these alloys in air at 1200°C. Upon cooling, the nonadherent scale spalls-off as a result of thermal stresses and is immediately ready for examination. The adherent oxide scales had to be extracted by the preferential dissolution of the alloy substrates in a bromine-methanol solution, which does not in any way affect the structure of Al2O3. The scales are then examined by scanning and replication electron microscopy. Figures 1, 2 and 3 are the top (gas surface), side and bottom views of these Al2O3 scales, respectively.