All the coatings and multilayer structures were deposited in a Sputron plasma-beam-sputtering apparatus at a temperature below 150 degrees C on polished alumina substrates (R(a)=25 nm) and polished tool steel discs. The coatings were annealed in an oxygen flow at temperatures in the range 500-850 degrees C. The oxidation kinetics of these coatings were studied by means of the weight gain as a function of the oxidation time at each temperature. On the same coatings, continuous in situ electrical resistivity measurements were taken and these indicate grain boundary oxidation. The composition and the depth profiles of the oxidation products formed were investigated using AES and XPS combined with sputter profiling. The oxide layers were found to grow according to a parabolic diffusion law with activation energies of 1.04, 1.89, 1.92, 2.37, 2.91 and 3.98 eV for Ti0.63Zr0.37N, TiN, CrN, ZrN, TiN/CrN and Cr0.72Ti0.28N, respectively.