Rates of oxidation of polycrystalline, (110), and (112) surfaces of iron have been measured at 24°, 100°, and 200°C by a manometric method using an initial oxygen pressure of about Torr. At the lower temperatures the relative rates of oxidation are found to be polycrystalline, (110), and (112) in decreasing order. At 200deg;C the different single crystal surfaces oxidize at essentially the same rate. Logarithmic rate laws are obeyed reasonably well for oxidations up to 200°C, at which point the oxidation rate, after a time, obeys a parabolic law. Using this parabolic rate constant for the oxidation of polycrystalline iron at 200°C, together with previous microbalance data for the low pressure oxidation of iron at 350° and 400°C (1), an activation energy of 32 kcal. mole−1 is found for the formation of magnetite on iron. Surface areas of polycrystalline and (112) surfaces have been measured before and after oxidation using the BET method, employing krypton adsorption at 77°K. It is found that the number of surface sites for the adsorption of krypton is dependent on the nature of the adsorbent surface.