Interfacial polycondensed composite membranes are well known for reverse osmosis. This study describes the preparation of interfacial polymerized composite membranes for gas separation obtained from new polyamides. The polymers were synthesized by derivates of terephthaloylchloride and commercially available multifunctional amines. The membrane polymers consist of linear or crosslinked chains. A high flux of carbon dioxide, 0.3 m(3) m(-2) h(-1) bar(-1), was observed, combined with a carbon dioxide/nitrogen selectivity up to 30. The permeability to hydrocarbons increased with hydrocarbon vapor concentrations. The synthesis of the thin polyamide layer was transmitted to a continuous production.