When surface potentials (or the surface charges) are high, the exponential term on the right-hand side of the Poisson-Boltzmann equation cannot be linearized. This nonlinear regime is systematically studied for various porous media and various physicochemical conditions. As in the linear regime, the numerical data for the electroosmotic coefficient when made dimensionless are shown to follow the semianalytical solution derived for a plane Poiseuille flow. Therefore, this coefficient can be deduced either from the specific surface or from the permeability and the formation factor. (c) 2006 Elsevier Inc. All rights reserved.