Oxidation kinetics of high purity polycrystalline Cr were measured at and . The reaction proceeded in two stages: an initial period of growth, in which the kinetics could be described with the Cabrera‐Mott theory, was followed by an abrupt transition to a lower growth rate and parabolic kinetics. The kinetic transition was accompanied by a change in diffraction pattern of the oxide from that characteristic of a random orientation of very fine grained to a pattern indicating a strongly preferred fiber texture. The oxide film formed in the pretransition region was flat whereas that formed in the posttransition region was composed of ridges and nodules separated by a very thin oxide film. Activation energies in both kinetic regions were much less than that found for self‐diffusion in . It is concluded that the rate‐controlling process throughout the reaction is metal transport via preferred pathways, such as grain boundaries, through the oxide film. In the pretransition region the density of such pathways is high, leading to uniform film thickening. In the posttransition region the density of such pathways is low, leading to localized transport and hence localized oxide growth.