The influence of small separate additions of aluminium, beryllium, chromium, magnesium, and silicon on the high-temperature oxidation of copper has been examined, these alloying elements having been chosen because their oxides have a high electrical resistivity. The composition and microstructure of the scales formed were studied and correlated with the rates of oxidation. The effectiveness of the additions in conferring oxidation-resistance was in the decreasing order: beryllium, aluminium, magnesium, silicon, chromium. Alloys having rates of oxidation less than that of copper showed divergences from the established parabolic and exponential laws. These divergences may be accounted for by a consideration of the relative rates of diffusion of copper and of the alloying element through the oxide layers.