Composite　membranes　consisting　of　microporous　tantalum-doped　silica　layers　supported　on　mesoporous　alumina　substrates　were　fabricated　using　chemical　vapor　deposition　(CVD)　in　both　thermal　decomposition　and　counter-flow　oxidative　deposition　modes.　Tetraethyl　orthosilicate　(TEOS)　was　used　as　the　silica　precursor　and　tantalum　(V)　ethoxide　(TaEO)　as　the　tantalum　source.　Amounts　of　TaEO　from　0　mol%　to　40　mol%　were　used　in　the　CVD　gas　mixture　and　high　H-2　permeances　above　10(-7)　mol　m(-2)　s(-1)　Pa-1　were　obtained　for　all　conditions.　Close　examination　was　made　of　the　H-2/CH4　and　O-2/CH4　selectivities　due　to　the　potential　use　of　these　membranes　in　methane　reforming　or　partial　oxidation　of　methane　applications.　Increasing　deposition　temperature　correlated　with　increasing　H-2/CH4　selectivity　at　the　expense　of　O-2/CH4　selectivity,　suggesting　a　need　to　optimize　membrane　synthesis　for　a　specific　selectivity.　Measured　at　400　degrees　C,　the　highest　H-2/CH4　selectivity　of　530　resulted　from　thermal　CVD　at　650　degrees　C,　whereas　the　highest　O-2/CH4　selectivity　of　6　resulted　from　thermal　CVD　at　600　degrees　C.　The　analysis　of　the　membranes　attempted　by　elemental　analysis,　X-ray　photoelectron　spectroscopy,　and　X-ray　absorption　near-edge　spectroscopy　revealed　that　Ta　was　undetectable　because　of　instrumental　limitations.　However,　the　physical　properties　of　the　membranes　indicated　that　the　Ta　must　have　been　present　at　least　at　dopant　levels.　It　was　found　that　the　pore　size　of　the　resultant　membranes　increased　from　0.35　nm　for　pure　Si　to　0.37　nm　for　a　membrane　prepared　with　40　mol%　Ta.　Similarly,　an　increase　in　Ta　in　the　feed　resulted　in　an　increase　in　O-2/CH4　selectivity　at　the　expense　of　H-2/CH4　selectivity.　Additionally,　it　resulted　in　a　decrease　in　hydrothermal　stability,　with　the　membranes　prepared　with　higher　Ta　suffering　greater　permeance　and　selectivity　declines　during　96　h　of　exposure　to　16　mol%　H2O　in　Ar　at　650　degrees　C.