Rates of oxidation of three heater alloys of nominal composition 80% nickel‐20% chromium were studied over the temperature range of 500° to 950°C and at a pressure of 7.6 cm of Hg of oxygen, using the vacuum microbalance method. Temper color films were obtained for all oxidations below 850°C, while gray or gray‐green films were obtained at temperatures of 850°C and higher. No evidence was found for scaling or cracking of the oxide from the alloys on cooling at temperatures of oxidation up to 950°C.