The oxidation of three iron‐nickel alloys nominally 30%, 41%, and 78% Ni was investigated over the temperature range of 600 °–1000 °C in controlled atmospheres with partial pressures of of 0.32 mm, 5.81 mm, and 26.3 mm. The gross effect of in the oxidizing atmosphere is to increase the oxidation rate (up to 13‐fold for the 30% alloy at 1000°C). In addition, at higher temperatures and higher , the rate‐determining diffusion process changes from the first half to the second half of the 60‐min reaction. The observed rates for the 30% and 41% alloy during the second phase are higher, while the second‐phase rate for the 78% alloy is lower. The Arrhenius plots for these alloys are not linear over the 600°–1000°C range. Below 800°C a low apparent activation energy, 30–40 kcal, is calculated, while above 800° a value in the 60 kcal range is obtained.