Recently, there has been improvement in membrane performance with respect to flux and salt rejection. There are high flux versions such as BL and NE90 showing 51gfd flux and 99% rejection, 76gfd flux and 97% rejection, respectively at 225psi and 2000ppm NaCl. The latest version of combining high flux and high rejection is called BLR, showing 39gfd flux and 99.5% rejection at 225psi and 2000ppm NaCl. If the flux of the above three membranes are compared with the standard membrane BE, the relative water permeability of the four membranes is increasing in the order of BE(1), BLR(1.5), BL(1.9) and NE90(2.8) under the same conditions. Likewise, the relative salt permeability is as follows: BE(1), BLR(0.77), BL(1.5) and NE90(5.4). In a real field application, a reverse osmosis (RO) system is not designed in such a way to utilize the maximum capacity of the high flux membrane. If it were so, then the membrane would be fouled very quickly. Instead, the high flux membrane is used at a pressure as low as possible to save the operating cost(electricity). The above membranes were used in simulation for producing 0.6MGD from a feed water having 1000ppm TDS. The operating pressure(psi) and permeate TDS(ppm) on each membrane used in the system design are shown as follows; BE(154psi and 17ppm), BLR(119psi and 11.2ppm), BL(100psi and 27ppm), and NE90(77psi and 157ppm). The results show that BLR is operated at a pressure 23% less than the standard membrane BE, meaning an energy consumption reduction of about 23% and a savings of about $60,000 per year. Moreover, BLR produced more pure(less TDS) water than BE. Likewise BL saves 35% energy and an operating cost of about $90,000 per year, but the quality of the permeate water (27ppm) is worse than BE. In the case of NE90, it reduces energy consumption by 50%, but this energy savings came at the expense of permeate TDS, increasing from 17ppm to 157ppm. Thus it appears that BLR is the best choice among the four membranes for both energy saving and higher purity of permeate water. Furthermore, a combination of BL and BLR enables the system to be operated at a pressure (103psi) similar to BL, yielding the quality of permeate water (19.9ppm) similar to BE. This combination is most promising since it saves on operating costs without sacrificing the quality of the product water. If it is willing to sacrifice the product water quality up to 100ppm, then a combination of NE90 and BLR could offer more energy saving than the combination of BL and BLR. Includes tables.