This report describes the preparation, properties, and utilization of inorganic membranes, primarily emphasizing the research and development aspects related to the separation of gases. Included are definitions, a brief historical background, a comparison of inorganic and polymeric membranes, a discussion of separation mechanisms, descriptions of various preparation or fabrication methods, studies and applications of inorganic membranes related to gas separations, and compilation of information on commercially available porous materials. The information is evaluated in terms of limitations, needs, and prospects for future development. The major types of gas transport through porous membranes are discussed in terms of viscous flow, free-molecule (Knudsen) flow, surface diffusion, capillary condensation, surface adsorption, ion exchange, and molecular sieving. Membrane preparation and fabrication techniques include: extrusion, powder suspension, molten salt inclusion, phase separation and leaching, nuclear track etching, dynamic deposition, anodic oxidation, pyrolysis, particle dispersion/slipcasting, and thin film deposition. Metallic, porous glass, ceramic, and metallic oxide membranes for separating various gases are tabulated. The needs for improved membrane materials, metal-to-nonmetal seals which will withstand high temperatures and pressures, and better membrane characterization techniques are discussed. 199 refs., 8 tabs.