The performance of a centrifugal membrane separation (CMS) system for reverse osmosis (RO) has been examined. In CMS the process pressure is developed at the periphery of a centrifuge rotor and the fluid cross-flow direction across the membrane surface is fixed with respect to the rotational direction. The influence of the rotating environment on RO flux has been determined fur different membrane orientations, and has been compared with conventional (non-rotating) pressure-driven RO separations of NaCl and MgSO4 solutions. At low salt concentrations the CMS system is equivalent to the conventional system, but shows progressive flux enhancement over conventional RO as the salt concentration of the feed-stream is increased. The extent of flux enhancement is maximized when the centrifugal force is directed away from, or in the plane of the membrane, and the fluid how is directed such that the Coriolis force on the bulk flow is away from the membrane surface. The Aux enhancement is related to a reduction in concentration polarization due to rotation induced instabilities which diminish the boundary layer thickness at the membrane interface.