The analytical model for a hollow- fiber reverse osmosis module reported previously was applied to commercial seawater desalination plants, to be verified by measured plant performance data. Membrane permeability constants were obtained from seawater desalination labo-tests with several hundred hollow fiber membranes. The permeability constants of Toyobo's hollow fiber membrane for seawater were nearly equal to those of sodium chloride solution. The osmotic pressures of seawater were estimated by a modified Miyake equation. Calculated results by the analytical model with the above parameters showed to be in good agreement with seawater desalination plant performance data.