In this study a range of commercial polyamide membranes intended for reverse osmosis service are compared. Significant differences in membrane chemistry are detected through the use of X-ray photoelectron spectroscopy. However, these changes did not translate into major differences in physico-chemical properties such as membrane roughness, contact angle or zeta potential. The permeability and rejection behavior of the membranes followed a classic tradeoff relationship, with high permeability leading to low rejection and vice versa. This tradeoff relationship persisted even after the membranes were fouled with alginic acid for 4 h. Conversely, the use of alginic acid in the presence of calcium led to more severe fouling. Under these conditions, cake enhanced osmotic pressure effects led to reductions in sodium rejection. The rate of fouling and the fall in rejection could be related to the initial flux through the membranes, which induces a higher drag force on the foulant species towards the membrane. (c) 2012 Elsevier B.V. All rights reserved.