Quite pure H is produced by passing steam and a hydrocarbon such as CH4 through a reaction zone packed with enough BaO to absorb all the CO2 formed, the zone is held at 1,750°-2,300° F. and at least 1 atm. absolute pressure. At least 8 parts by weight of BaO for each part of C in the hydrocarbon gas is provided. The BaO is regenerated by heating in a fluidized bed at 2,300°- 2,350° F. The best results are obtained when the reaction is carried out at 1,750°-2,050° F. and 20-50 atm. and when the steam: hydrocarbon ratio is 2:1 to 4:1.