The development of commercial RO membranes offering high salt rejection and flux has focused more attention on improving desalination process technology. The energy-efficient reverse osmosis (EERO) process has recently been advanced that combines single-stage reverse osmosis (SSRO) with a countercurrent membrane cascade with recycle (CMCR). The SSRO retentate is the feed to the CMCR that employs countercurrent retentate and permeate flow, permeate recycle, and retentate self-recycling via the use of NF membranes in one or more stages. This reduces the foulant load on the RO stage in the CMCR and allows it to run at a higher recovery than conventional SSRO. This option as well as the effects of pump and energy-recovery device (ERD) efficiencies are considered here. For a typical 35 g/L seawater feed and 035 g/L water product, the 4-stage EERO process reduces the osmotic pressure differential (OPD) relative to conventional SSRO by 50% at all overall water recoveries. For pump and ERD efficiencies of 85% and 90%, respectively, the 3-stage EERO process has a 50% overall water recovery at an OPD of 42.7 bar and a net specific energy consumption (SECnet) of 2.323 kWh/m(3), thereby reducing the OPD by 23.1% at the cost of increasing the SECnet by only 3.6% relative to conventional SSRO. For the same efficiencies the 4-stage EERO process can achieve a 75% overall water recovery at an OPD of 55.5 bar and SECnet of 3.773 kWh/m(3), thereby reducing the OPD by 50% and the SECnet by 3.6% relative to conventional SSRO at that recovery. (C) 2015 Elsevier B.V. All rights reserved.