Step-type Pt/gamma-Al2O3 catalyst pellets were prepared by coimpregnation and sequential impregnation of hexachloroplatinic and citric acids. A diffusion-adsorption model based on Fickian diffusion and Langmuir adsorption was formulated. The parameters of the model were determined from separate experiments. Adsorption constants were obtained in the absence of diffusional resistances, while effective diffusivities were obtained in the absence of adsorption or desorption. In order to extend the Langmuir adsorption equations to the multicomponent system, two new parameters were introduced, which accounted for solution effects and steric hinderances. Catalyst distribution inside the pellet and the effects of various impregnation parameters were predicted satisfactorily by the multicomponent diffusion-adsorption model. The platinum distribution of pellets prepared by the two impregnation techniques was similar, although sequential impregnation gave thinner catalyst step widths.