In this work high quality cobalt oxide silica membranes were synthesized on alumina supports using a sol gel, dip coating method. The membranes were subsequently connected into a steel module using a graphite based proprietary sealing method. The sealed membranes were tested for single gas permeance of He, H-2, N-2 and CO2 at temperatures up to 600 C and feed pressures up to 600 kPa. Pressure tests confirmed that the sealing system was effective as no gas leaks were observed during testing. A H-2 permeance of 1.9 x 10(-7-) mol m(-2) s(-1) Pa-1 was measured in conjunction with a H-2/CO2 permselectivity of more than 1500, suggesting that the membranes had a very narrow pore size distribution and an average pore diameter of approximately 3 angstrom. The high temperature testing demonstrated that the incorporation of cobalt oxide into the silica matrix produced a structure with a higher thermal stability, able to resist thermally induced densification up to at least 600 degrees C. Furthermore, the membranes were tested for H-2/CO2 binary feed mixtures between 400 and 600 degrees C. At these conditions, the reverse of the water gas shift reaction occurred, inadvertently generating CO and water which increased as a function of CO2 feed concentration. The purity of H-2 in the permeate stream significantly decreased for CO2 feed concentrations in excess of 50 vol%. However, the gas mixtures (H-2, CO2, CO and water) had a more profound effect on the H-2 permeate flow rates which significantly decreased, almost exponentially as the CO2 feed concentration increased. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.