The objective of this research was to determine the effect of vanadium alloy additions on the oxidation behavior of cobalt-nickel alloys. Eighteen alloys were reacted with o2 at 0.5 Atmosphere and 1,351 deg., 1,389 Deg., and 1,429 deg. K. The alloy compositions consisted of co-ni master alloys (o, 22, 50, 70, 91, and 100 weight percent ni) with V additions of 0, 0.9, and 2.7 Weight percent. Large early deviations from, or changes in, the parabolic rate constant were encountered, but the reaction rate in most cases declined approximately in accordance with the parabolic rate law. Relatively, the vanadium degraded the oxidation resistance most at the highest nickel contents. In some cases, melting of the oxide was inferred from microscopic evidence and x-ray diffraction measurements disclosed the presence of low-melting vanadates.