Hydrogen-permselective membranes were synthesized by chemical vapor deposition of SiO2, TiO2, Al2O3, and B2O3 layers within the pores of Vycor tubes. The deposition involved reaction of SiCl4, etc., with water at 100-800 °C depending on the chloride and the reaction geometry. Permselective SiO2 layers could be formed in either the one-sided or the two-sided (opposing reactants) geometry, while deposition of TiO2 and Al2O3 layers was achieved only in the two-sided geometry. The permeation coefficients at 450 °C were 0.3 and 0.1 cm3/(cm2·min·atm) for SiO2 membranes produced in the one-sided and two-sided geometries, respectively. The H2:N2 permeation ratios were 1000-5000. The TiO2 and Al2O3 membranes had somewhat lower permeation coefficients and H2:N2 ratios. The membranes were characterized by scanning electron microscopy (SEM) and electron microprobe analysis (EMA). A reaction mechanism is suggested involving heterogeneous reactions of chloride and water molecules with hydroxyl and chloride groups in the growing deposit layer.