The rapid development in reverse osmosis (RO) membrane technology has led to the development of many new membrane products. In this study pilot tests were conducted on two new RO membranes to determine the improvement from the older generation RO membranes. This paper presents the results of pilot testing conducted on these new generation low pressure brackish water RO membranes for groundwater desalination. Two new membranes were tested - ESPA 4 manufactured by Hydranautics, Inc, Oceanside, California and RE 4040 BL manufactured by Saehan Industries, South Korea. Phase I testing included pilot testing an older generation membrane (ESPA 2 from Hydranautics) to establish a baseline. It was found that the new generation membranes operated at a lower operating pressure than the older generation membrane by 20-30%. The salt rejections were lower for the new generation membranes by 0.7-1.8%. During this phase it was found that of the two new generation membranes the RE 4040BL membrane had a slightly lower operating pressure and higher rejection than the ESPA 4 and it was selected for Phase II of the testing. During the second phase of the testing the RE 4040BL membrane was operated at a flux of 20 gfd and at recoveries between 75% and 90% to observe the effect of these aggressive operating conditions on the fouling behavior of the membrane. No significant fouling was observed under these conditions. Model simulations on both the new generation membranes were performed and results are presented in this paper. Also capital and operating cost estimates have been presented comparing the new generation membrane with the older generation membrane for a currently operating 4 mgd plant. Includes tables, figures.