Surface roughness plays a dominant role in increasing the oxidation rate of metals and alloys during erosion compared to the oxidation rate in static air. Ni and Ni-20Cr were eroded at two different impact velocities (35 and 65 m/s) and for two different impact angles (90° and 30°). The eroded samples were subsequently isothermally oxidized in static air at three different test temperatures. The increased oxidation kinetics in the case of Ni could be explained on the basis of increased roughness caused by erosion prior to oxidation. In the case of Ni-20Cr, the effect of increased roughness on oxidation was largely offset by the fact that the number of grain-boundary diffusion paths decreased due to coarsening of the grains of the oxide scale.