Triheptyl cellulose (THC)/ethyl cellulose (EC) (3/97) binary blend membranes were prepared from tetrahydrofuran (THF), chloroform and dichloromethane solutions and their oxygen enrichments were studied at different temperatures and operating times. With increasing temperature from 298 to 358 K, the flux Q(OEA) and permeability P-OEA of oxygen-enriched air (OEA), the oxygen permeability P-O2 and the oxygen concentration Y-O2 in the OEA and the actual oxygen/nitrogen separation factor (ASF) through the membranes all increase. These oxygen-enrichment properties are better for the THC/EC membrane than for the THC-free pure EC membrane cast from the same THF. Moreover, the three THC/EC membranes show an interesting concurrent increase in the Y-O2 and Q(OEA) with increasing temperature. It is found that the efficiency of enriching oxygen through the THC/EC membrane varies slightly after 80 h of operation. The magnitudes of the Q(OEA) and Y-O2 for a 17 mu m-thick THC/EC membrane cast from THF are 6.7 x 10(-4) cm(3) (STP)/s cm(2) and 38.8%, respectively, at 358 K and transmembrane pressure difference of 0.41 MPa in a single step. The ordered supermolecular arrangement of the cholesteric liquid crystalline THC may be responsible for these results. Additionally the oxygen-enriching ability depends slightly on membrane-forming solvents.