Substantially pure oxygen is provided to an up flow reformer (49a) from a separator (108) downwardly impelled water droplets (53) mix with the outflow (58) of a CPO (59), flowing upwardly through high temperature (68) and low temperature (73) water gas shift reactors. The reformer output flows through a mixer (79) to a down-flow PrOx containing two beds (82, 94) of preferential CO oxidation catalyst therein. A series of compressors (120-122) compress water and carbon dioxide out of the gaseous flow to provide pure, pressurized hydrogen. Oxygen (111) is separated (105, 108) from nitrogen (112).