NO x adsorption-desorption experiments were carried out on a series of W-free and W-containing ZrO 2 samples. To the best of our knowledge, this study establishes for the first time NO x -TPD (temperature-programmed desorption of NO x ) as a reliable method to estimate the accessible ZrO 2 surface of complex oxides. The NO x uptake by ZrO 2 was found to be 5.8 ( 0.2 µmol/m 2 . On the tungstated zirconia series of samples, the NO x uptake decreases linearly with W density up to about 5 W/nm 2 , which is in excellent agreement with literature data for which the pseudo monolayer coverage was obtained by spectroscopic methods. The accessible ZrO 2 surface area of ZrO 2 /SBA-15 materials, which cannot be ascertained through common spectroscopic methods, was estimated by WO 3 thermal spreading and the NO x -TPD method. Both values compare very well but NO x -TPD, unlike WO 3 thermal spreading, does not alter the integrity of the investigated sample as the sample is pretreated at lower temperatures (500 instead of 700°C).