A pressure vessel (PV) which contains the membrane elements of seawater reverse osmosis (SWRO) desalination has been modeled using analytical solution and finite element modeling (FEM) to optimize the PV design parameters. Two types of PV materials have been compared namely; stainless steel and fiber reinforced composite materials. Von-Mises yield criterion and Tsai-Wu failure criterion are used for the design of stainless steel and composite PVs respectively. E-glass/epoxy and carbon/epoxy composite materials are considered in this work. In addition, hybrid composite materials are introduced for layers through the vessel thickness. The results have shown that the optimum lay-up is achieved using the angle-ply [+/- circle minus](ns) at winding angle of 54 degrees for E-glass/epoxy and 55 degrees for carbon/epoxy PVs while for hybrid composite PVs the optimum lay-up is [90G/+/- 50C/90G](ns). Also, the results have shown that the composite PVs have lighter weight than the stainless steel PVs. The carbon/epoxy PVs introduce the optimum weight savings but in terms of the total PVs cost, the hybrid composite PVs can be used. (C) 2016 Elsevier B.V. All rights reserved.