The oxidation behavior of films of varying composition was studied using x‐ray photoelectron spectroscopy (XPS). At 500°C and under of oxygen, preferential oxidation of cobalt over nickel was observed in the alloys, although pure cobalt and pure nickel showed similar oxidation kinetics. The cobalt oxide, identified as , grew parabolically at a rate dependent on the alloy composition. Oxidation‐induced segregation of cobalt at the surface was also observed in the alloys.