In this work a comparison is made between values of the metal surface areas of several alumina-supported Ru, Rh, and Pt catalysts obtained by hydrogen adsorption isotherms, here defined as the "Multiple Introductions" method, and those calculated by a very simple technique defined as the "Single Introduction" method. With the systematic application of the procedure designated "Back-Sorption," particularly good agreement is observed between the two techniques if dispersion is calculated on the basis of the irreversibly adsorbed hydrogen. "Back-Sorption" is a necessary practice because of the presence on the above-mentioned metals of more than one adsorbed species not to be considered for the calculation of dispersion, as shown in a more detailed manner for a Pt/Al2O3 catalyst using temperature-programmed desorption. Whenever the conditions for its applicability are satisfied, the Single Introduction method provides a faster and more reliable way to measure the dispersion of metal-supported catalysts than the Multiple Introductions technique.