The effects of impurity atoms on the oxidation of aluminum have been studied. Selected impurities were introduced by ion−implantation to a depth of 400 Å prior to the anodic growth of oxide in both oxalic acid and ammonium pentaborate solutions. Oxygen uptake and impurity movement during oxidation were studied using Rutherford backscattering of He+ ions. Correlation was observed between movement of the implanted species and oxygen uptake. Certain impurities (e.g., Bi and Pb) were found to enhance oxidation whilst others (e.g., Au and Cu) reduced the oxidation rate. The results are consistent with the oxide behaving as an n−type semiconductor with electron transport being rate determining. The effect of radiation damage during ion−implantation was shown to be of secondary importance.