A series of solvent resistant polyimide membranes, with nominal molecular weight cut-offs (MWCO) between 230-700 Da, are evaluated through high pressure filtration of six solutes dissolved in toluene. These solutes range in MW from 142 to 311 Da, and include normal and branched alkanes, and aromatic compounds. The asymmetric membranes, made from a copolymer of benzophenone tetracarboxylic acid with toluene diisocyanate and methylene bis(phenyl isocyanate), shows preferential transport of straight chain over branched alkanes, and of aromatic over non-aromatic compounds. The normal alkanes allow for estimation of MWCO. Performance curves are generated for this family of polyimide membranes. Transport rates, in mm/h, are determined for each dissolved component based on a solution-diffusion equation. These rates are then used to predict membrane performance under alternative conditions of pressure and composition. The results are consistent over the whole range of MWCO's with the membranes acting in a solution-diffusion mode. These membranes have industrial utility in the enrichment of aromatic streams and in nanofiltration applications.