The oxidation of the chemically etched Ge(001) surface has been investigated by means of kinetic resolved X-ray photoelectron spectroscopy (KRXPS). In situ oxidation treatments have been carried out at T=250°C, under 0.5 atm of pure oxygen atmosphere and for different durations. We propose a two step oxidation model. First, the bare portions of the surface are oxidized. Then, follows a lateral growth of the germanium oxide islands. The process is assisted by the decomposition of the overlayer that stems from the chemical etching and the air contamination. The model gives a consistent interpretation of the KRXPS measurements.