Quantitative X-ray photoelectron spectroscopy was used to characterize the native oxide film formed on 42CrMo4 steel surface by air exposure in normal conditions. In order to determine the thickness and composition of the oxide layer we have used a stacking layer model together with experimental XPS sputtering depth profiling. At a nanoscale study, to obtain quantitative results one must take into account fundamental parameters like the attenuation depth of photoelectrons. We have found that both lepidocrocit (gamma-FeOOH) and magnetite (Fe3O4) were present and the total thickness of the oxide layer was 16 monolayers. (C) 2008 Elsevier B.V. All rights reserved.