We have developed defect-free asymmetric hexafluoro propane diandydride (6FDA) durene polyimide (6FDA-durene) hollow fibers with a selectivity of 4.2 for O-2/N-2 and a permeance of 33.1 X 10(-6) cm(3) (STP)/cm(2)-s-cmHg for O-2. These fibers were spun from a high viscosity in situ imidization dope consisting of 14.7% 6FDA-durene in a NMP solvent and the inherent viscosities (IV) of this 6FDA-durene polymer was 0.84 dL/g. Low IV dopes cannot produce defect-free hollow fibers, indicating a 6FDA-durene spinning dope with a viscosity in the region of chain entanglement seems to be essential to yield hollow fibers, with minimum defects. The effects of spinning parameters such as shear rates within a spinneret and bore fluids as well as air gap on gas separation performance were investigated. Experimental data demonstrate that hollow fibers spun with NMP/H2O as the bore liquid have higher permeances and selectivities than those spun with glycerol as the bore liquid because the former has a relatively looser inner skin structure than the latter. In addition, the selectivity of hollow fibers spun with NMP/H2O as the bore liquid changes moderately with shear rate, while the selectivity of hollow fibers spun with glycerol are less sensitive to the change of shear rate. These distinct behaviors are mainly attributed to the different morphologies generated by different bore fluids.