The placement of a surface with ionogenic groups in water may lead to the generation of an electrical double layer. The electrical double layer may make a significant contribution to aqueous solution processes such as in-terfacial ion adsorption, flocculation, and coagulation. As a means of characterizing the electrical double layer, surface associated electrostatic potentials are frequently measured, including flat plate streaming potentials (6 potentials), potentials obtained from the electrophoretic mobility of colloid spheres (£ e potentials), and diffuse layer potentials () derived by fitting DLVO theory to surface force versus separation curves. 1 One contentious issue is whether or not it can be assumed that these various electrostatic potentials are equivalent. In this work, we take a model system and compare potentials, ß potentials, and values derived from the force versus separation curves for the interaction of a colloid sphere with a flat plate (measured with an atomic force microscope). The model system is comprised of