The permeances of several gaseous species (He, H2, CO2, N2, CH4, and C2H4) were measured through silica hollow fiber membranes over a temperature range of 298 to 473 K at a feed pressure of 20 atm. Permeances ranged from 10 to 2.3∗ 105 Barrer/cm at 298 K and were inversely proportional to the kinetic diameter of the penetrant. The permeance of gaseous species were found to decrease with decreasing differential pressure driving force at AP <5 bar. No pressure dependency was found at AP > 5 bar. Mass transfer through the silica hollow fiber membrane was found to be an activated process. Activation energies for diffusion through the silica membrane calculated from the slopes of Arrhenius plots of the permeation data ranged from 4.61 10 14.0 kcal/mole and correlate well with the kinetic diameter of the penetrants. Large separation factors were obtained for the penetrants. The separation factors decreased with increasing temperature. The CH4/CO2 mixed separation factors were higher than the values calculated from pure gases at temperatures below 373 K. This behavior was observed after the membrane had been heated to at least 398 K and then cooled in an inert gas flow. The differences between the mixture and ideal separation factors is attributed to a competitive adsorption effect in which the more strongly interacting gases saturate the surface and block the transport of the weakly interacting gases.