Four different methods for Pd dispersion measurement are compared: H-2 adsorption, O-2 adsorption, H-2 titration, and O-2 titration. A correct comparison requires the knowledge of H/Pd-s and O/Pd-s stoichiometries. The H/Pd-s stoichiometry is discussed by reviewing published results, which lead us to the conclusion that H/Pd-s = 1. Our experimental results demonstrate that the relative O/H stoichiometry is independent of Pd concentration, type of carrier, and preparation method, O/H = 1; thus O/Pd-s = 1. If correctly performed, the four methods give the same Pd dispersion, but those based on direct adsorption have less applicability, because they require the complete removal of hydrogen used for reduction from the metal surface. A method to evaluate residual hydrogen is given.