A concept demonstration has been made to simultaneously enhance both O-2 and CO2 gas permeance and O-2/N-2 and CO2/CH4 selectivity via intelligently decoupling the effects of elongational and shear rates on dense-selective layer and optimizing spinning conditions in dual-layer hollow fiber fabrication. The dual-layer polyethersulfone hollow fiber membranes developed in this work exhibit an O-2/N-2 selectivity of 6.96 and an O-2 permeance of 4.79 GPU which corresponds to an ultrathin dense-selective layer of 918 angstrom at room temperature. These hollow fibers also show an impressive CO2/CH4 selectivity of 49.8 in the mixed gas system considering the intrinsic value of only 32 for polyethersulfone dense films. To our best knowledge, this is the first time to achieve such a high CO2/CH4 selectivity without incorporating any material modification. The above gas separation performance demonstrates that the optimization of dual-layer spinning conditions with balanced elongational and shear rates is an effective approach to produce superior hollow fiber membranes for oxygen enrichment and natural gas separation. (c) 2008 Elsevier B.V. All rights reserved.