Supported mesoporous gamma -Al2O3 membranes deteriorate and blister in steam-containing environments at high temperatures. This deterioration led us to the development of a new type of supported gamma -Al2O3 membrane with significantly improved stability under hostile conditions. Two measures were taken to achieve this result. First, the gamma -Al2O3 itself was stabilized by an addition of 6 mol % La2O3 to suppress pore growth of the mesoporous structure. Second, the adherence of the gamma -Al2O3 membrane to the alpha -Al2O3 support was significantly improved by application of phosphate bonding between the membrane layer and the support, using an Al(H2PO4)(3) precursor solution. Membranes applied without phosphate bonding were separated from the alpha -Al2O3 support during high-temperature steam treatment, resulting in complete loss of separative properties. The newly developed membranes could be operated for 100 h at 600 degreesC in H2O/CH4 = 3/1 (bg volume) at 2.5 MPa total pressure with no delamination or cracking in the membrane-support interface and with no significant pore growth in the gamma -Al2O3 membrane.