Oxide ridges formed during the transient stage oxidation of the scale evolution in iron alloys containing 22 wt % Cr that were held at 800 degrees C in dry air. The surface oxidation process was imaged in situ through a confocal scanning laser microscope, and the results were correlated with postexperiment characterization through scanning electron microscopy and the DualBeam system (focus ion beam and electron beam) analysis combined with three-dimensional reconstruction. The oxide ridges that formed on top of the Cr oxide scale overlapped the intersections of the underlying alloy grain boundaries with the Cr oxide scale. Ridges were generally very small on grain boundaries with disorientation angles of less than 15 degrees, and it was suggested that the boundaries of the surface grains in the alloy may serve as bottlenecks for the transport of scale-forming elements. The effects of La (120 and 290 ppm) and Ce (270 and 610 ppm) additions during melt-stage processing were also investigated.