We present a self-consistent continuum 3-D simulation of ion permeation through the ompF porin channel, a protein found in the membrane of the e-coli bacterium. The model is based on the simultaneous solution of Poisson's equation, which captures Coulomb interactions and a continuity equation for each ion species, describing permeation down an electrochemical gradient. Water is treated as a uniform background medium with a specific dielectric constant and macroscopic current flow is resolved by assigning an appropriate mobility/diffusivity to each ionic species. Using this model with a single diffusivity for each ion species we predict the current-voltage relations for ompF porin for a wide range of experimental conditions. Agreement with experimental measurements is remarkably good given that the model uses the same two adjustable parameters (diffusivity for each ion species) for the entire set of experimental conditions.