A study was made of the effect of surface preparation and pretreatment on the oxidation of zone‐refined nickel from 500° to 700°C. “Clean,” hydrogen‐reduced surfaces, maintained essentially free of impurities such as S, Si, Fe, and C, oxidized at a faster rate than air‐exposed electropolished or etched annealed nickel. At 700°C, the rapid rate, arising from a high leakage path density in the oxide, resulted in the formation of voids at the metal‐oxide interface. The oxidation rate of electropolished and etched specimens was strongly dependent on substrate orientation and this anisotropy, responsible for a slower average oxidation rate, reflected varying contributions of leakage path diffusion. Very thin oxides, as on nickel orientations near (112) after electropolishing, formed primarily by lattice diffusion and the parabolic rate constant at 600°C was ∼104 lower than for the thickest oxides. Correlation with other studies in the laboratory indicates that the activation energy for the growth of on Ni is ≥52 kcal·mole−1 for lattice diffusion and approximately 37 kcal·mole−1 for leakage path diffusion.