To study the electrokinetic behavior of highly charged colloidal particles, we used monodisperse oil drops suspended in water and stabilized with a surfactant, sodium dodecylsulfate. Results from dynamic light scattering, conductivity, and electrophoretic mobility measurements show that the emulsion particles have high zeta-potentials, corresponding to a large density of surfactant ions on the surface. Attempts to reconcile results from mobility and conductivity measurements using the standard electrokinetic model were unsuccessful. The inadequacy of the standard model is ascribed to the high surface potential of the droplets and attendant changes in the counterion density and properties of the inner part of the diffuse layer.