The strength and stability of passive films produced on stainless steel by various passivating treatments have been evaluated. In addition, electron diffraction has been applied to the study of passivated stainless steel surfaces and of bulk oxide films. Break‐through‐potential data and confirmatory immersion‐corrosion data showed that no passivation treatment confers lasting protection to stainless steel immersed in media which corrode the unpassivated metal. Equally effective results were obtained with stainless steel which was cleanly pickled, thoroughly rinsed, and air dried. Although no definite evidence of the existence of passive films was found by reflection electron diffraction studies, bulk oxides produced by chemical or air oxidation on 18‐8‐S stainless steel were found to consist chiefly of with no nickel oxide and little iron oxide present. The bulk oxides formed by air oxidation on straight chromium‐iron alloys consisted of , , , and mixtures of these oxides.