The orthogonal collocation technique has been applied to the development of a numerical solution of the unequal distances of closest approach (UDCA) theory for any number of electrolytes and planes of closest approach to the electrode surface. On the basis of theoretical analysis of the reaction coordinate of Zn2+ reduction by Schmickler et al. (Chem. Phys. 2000, 252, 349), a UDCA analysis of the Frumkin effect on the bserved charge-transfer rate constants has been performed. The supporting electrolytes LiClO4, Mg(ClO4)(2), and Al(ClO4)(3) were chosen to vary systematically the distance of closest approach of the electrolyte cation with respect to that of the electroactive species. UDCA distances of closest approach derived from electrocapillary data are shown to provide a reasonable account of the Frumkin effect. However, more consistent results are obtained when variations of the Zn2+ activity coefficient, computed from the MSA theory, are also considered.