Herein we report the preparation of polysulfone (PS) membranes using a CO2-assisted phase inversion method. The effect of the solvent affinity and depressurization rate in the morphology and in the performance in terms of pure water flux of the membranes has been investigated. Different casting solutions were prepared using the following solvents: methylpyrrolidone, dimethylformamide, dimethylacetamide, chloroform, dimethylsulfoxide and dimethylpropionamide. The morphologies of the membranes obtained by fast (less than I min) and slow (approximately I h) depressurization have been compared. These parameters had a significant effect upon the pore size and on the water fluxes of the membranes. A schematic ternary diagram of the system polymer-solvent-CO2 is discussed. (c) 2006 Elsevier B.V. All rights reserved.