Two new thin-film composite reverse osmosis membranes have been developed with exceptional properties for processing feedwaters having high osmotic pressure [>34 L/m 2-h (20 gal/ft 2-d), >99% salt rejection at 2,760 kPa (400 psi) net] or low osmotic pressure [>34 L/m 2-h (20 gal/ft 2-d), >97% salt rejection at 1,380 kPa (200 psi) net]. The membranes have sufficient chlorine tolerance (>1,000 ppm-h) to withstand exposure to chlorinated water that has been incompletely dechlorinated. They are contained in spiral-wound elements of 1.5-m Magnum® length as well as conventional 1.0-m legth. Stable element performance is demonstrated over broad ranges of pH and pressure and by long-term tests.