The oxide layers formed on Fe‐26Cr alloy are wrinkled, porous, and blistered, and the metal/oxide interface markedly roughened. This is interpreted as evidence that compressive stresses are generated continuously in the growing oxide, hence that anion diffusion participates in the growth process. Smooth oxidation curves are observed if the wrinkled scale is adherent, even though non‐uniform. However, when blistering and cracking occurs, as with electropolished specimens, the weight‐gain/time curves are irregular. Similar irregularities occur wih Fe‐26Cr‐0.5 Si, Fe‐26Cr‐1Mn, type 446 and pure Cr. Manganese decreases oxidation resistance.