On the basis of the critical analysis of the NOx-TPD data obtained on WOx-ZrO2 samples [Law, H. Y.; Blanchard, J.; Carrier, X.; Thomas, C. J. Phys. Chem. C 2010, 114, 9731], this work provides convincing arguments for the first time upon which calculation of W surface density should be done by correcting the specific surface area of the samples for the content of W as WO3, rather than by the straightforward manner used in most studies reported to date. The use of this particular calculation method allows reconciling some of the literature data, which, at first sight, seem to be incoherent. Consequently, authors must be aware that comparisons with literature data should be made with the greatest concern, regarding the method used to calculate W surface density in particular.