The trend of investment and water cost in RO seawater systems is being evaluated. The cost data used for this evaluation are based on published information from operation of actual RO seawater installations and recent studies. The effect on process economics of major design parameters: recovery rate and feed water salinity based on three representative seawater water sources: Mediterranean, Atlantic and Pacific Ocean on energy consumption is analyzed, The objective of this evaluation is to determine economic feasibility of operating of seawater systems at higher recovery rates versus process optimization based on prevailing economic parameters. The optimized system design will be compared with the design of recent large seawater installations: 10,000m(3)/d plant at Eilat Israel, 40,000m(3)/d seawater plants at Larnaca, Cyprus and the design proposed for the 95,000m(3)/d RO plant at Tampa, Florida.