Hydrogen or gas mixtures containing hydrogen are obtained by the alternate passage of hydrocarbon gas, with or without the addition of steam, and air through a bed of highly heated coke or refractory material, the air being supplied at different levels within the bed or in different amounts at different levels. Air is passed into a heat regenerator 7, through a valve 14, through regulating valves 16 on tuyeres 13 and into a coke bed 2 where it burns the carbon deposited during the previous run and some coke. The "blow" gases thus formed enter a combustion chamber 12 <PICT:0340050/III/1> where they are burnt by preheated secondary air entering through pipe 10. The valves 11, 3, 6 and 14 are then closed and the valves 4, 5, 9 and 15 opened, 9 to a small extent. Hydrocarbon gas, with or without steam passes through the heated regenerator 8, is decomposed by the hot coke 2 and passes out through valves 15 and 9, the portion passing through 9 preheating the fresh coke and that passing through 15 heating the regenerator 7 and escaping through valve 5. The regenerator 7 should be purged before and after each blow with steam or combustion gases. A heat exchanger may be provided instead of a regenerator, two plants being connected to the same heat exchanger. Specification 328,642, [Class 55 (i), Coking &c.], is referred to.