Nanofiltration (NF) membranes are capable of highly rejecting divalent anions (e.g., sulfate) while retaining a large portion of monovalent anions (e.g., chloride) from seawater. NF is thus a potential technology to provide nearly sulfate-free seawater for oil fields water injection operations. However, as the case with any pressure-driven membrane processes, concentration polarization is the most critical problem encountered in NF operation. For proper design and operation of NF for selective removal of sulfate from seawater and the like of saline streams, knowledge of ions concentrations at the membrane surface and on the concentrate side of the membrane is critical. This second article, in a four-part series, provides a modeling tool to analyze the effect concentration polarization phenomena in NE Such an analysis allows the prediction of the actual rejection (R-a) in the absence of concentration polarization, and the accumulation of rejected ions at the membrane surface (C-m).