In this work a straightforward procedure for the optimum design and operation of the seawater reverse osmosis (SWRO) plants is being proposed. The analysis is based on analytical equations for the permeate flow rate and quality and the salt flow rate. The mathematical model and the developed software can predict the brine and permeate characteristics for any SWRO plant regardless of the number of the membrane modules in the pressure vessels. The results of the developed 3 software were verified by experimental data from a 280 m(3)/d RO plant, with 8" membrane module made by FilmTec, and they were compared with the predictions made by ROSA 6.0 software. An excellent agreement was observed between the prediction of the suggested model and the experimental data. The model can be applied in any type of membrane modules as long as the geometry and the membrane characteristics are known. Different operating conditions were tested and an effort was made for the optimum design and operation of the plant so that the minimum specific energy consumption can be achieved. It is believed that the analytical model presented in this work is a very useful tool not only because of its accuracy for the SWRO plant design and operation but also because of its simplicity.