The formation of oxides at 400 °C and 90 °C with two different oxygen concentration conditions on carbon steel surface was studied. From 400 °C tests, oxide films were observed in both conditions. The oxide formed on the surfaces which were exposed to an atmosphere with no change in O2 concentration was Hematite. On the surfaces which were exposed to an atmosphere with change in O2 concentration, Magnetite and Hematite were found due to the different exposure time and different conditions of the apparatus. The thickness of the oxide film formed on each membrane was calculated from the weight gained by the membrane and the kinetics of oxide formation on each condition was modelled. From the 400 °C exposure, the reaction rate was controlled by diffusion of O2 through the oxide layer. The diffusivity of oxygen through the oxide layer, DO2, was calculated from the rate of oxide formed on the surfaces which were exposed to an atmosphere with no change in O2 concentration and was found to be DO2 = 7.055×10-14 m2/s and the parabolic rate constant, k = 1.089×10-17 m2/s. DO2 was used in the prediction of oxide form in the atmosphere with changing O2 concentration. From the 90 °C exposure, weight gains on the membranes were not significant and no oxide films were observed.