Nonpolar colloidal dispersions are used as inks for electrophoretic development of electrostatic latent images. The need for a modification of the classical relation between the charge and the zeta potential of particles in these dispersions is confirmed by an independent experimental determination of the particle charge and mobility, using the series-capacitor technique introduced in a previous publication. In addition to the charged toner particles, the inks contain surfactant micelle ions of both polarities with their mobilities, in general, differing by orders of magnitude. It is shown that, in spite of this complex com position of charge species, it is possible to obtain an estimate of the density and mobility of each species from an accurate interpretation of experimental results based on the theoretical model of the technique.