The theories of the linear sweep voltammetry (LSV) and cyclic voltammetry (CV), including branch cyclic voltammetry (BACV), of a mixture containing two components whose electrode processes are reversible and independent are described. The digital simulation method is used to simulate the theoretical linear sweep and cyclic voltammograms at spherical electrodes. A mixture of Pb2+ and Cd2+ at hanging mercury drop electrodes is used to test the theories. Both theory and experiment show that, in the presence of a species which is reduced at more positive potentials, it is difficult to determine the concentration of another species; considerable error could be caused in LSV, but CV based on the reverse branch of a cyclic voltammogram and BACV show less error. The allowed concentration of the more positively reduced species with a 10% relative error in CV and BACV is about four to twenty times more than that in LSV. However, in the presence of a species that is reduced at more negative potentials, LSV shows far less error than BACV and CV. The theoretical and experimental results are consistent.