In the present work, in situ X-ray diffraction (XRD) was used to identify the oxides formed on the AISI 316L stainless steel (SS) during isothermal oxidation at 1000 degrees C, in air. The results were compared with those obtained on the AISI 304 SS in order to better explain the role of molybdenum on the oxidation process of the AISI 316L (containing 2% Mo). A good oxidation behavior is observed on the AISI 316L considering kinetics, structural characteristics and scale adherence. It is shown that molybdenum plays a similar protective role as the one observed with silicon. Moreover, it is possible to add a higher content of molybdenum in the stainless steel compared with silicon (usually 0.5wt%). This higher protective element content hinders the external iron diffusion and leads to the lower growth rate and the better scale adherence. The oxide scale is then composed of Cr2O3 with a small amount of Mn1.5Cr1.5O4 at the external interface. The better scale adherence appears to be also related to a pegging effect at the internal interface. (C) 2008 Elsevier B.V. All rights reserved.