In this paper, we present the general equations for facilitated ion transfer reactions across oil vertical bar water interfaces based on different competitive ligands, i.e., the transfer of a cation that, under given conditions, is assisted by a mechanism that involves ligands exchange. The obtained results agree with the general voltammetric criteria reported by Girault and co-workers [F. Reymond, P.-A. Carrupt, H.H. Girault, J. Electroanal. Chem. 449 (1998) 49; F. Reymond, G. Lagger, P.-A. Carrupt, H.H. Girault, J. Electroanal. Chem. 451 (1998) 59] for the facilitated transfer of a unique cation assisted by a neutral ligand. The equations reported in this paper grant to simulate the system under all possible conditions. The results are interpreted for different zones determined by the ratio of cation and ligand concentrations. (c) 2005 Elsevier B.V. All rights reserved.