Steam reforming system having a steam cracker and a steam reformer. The steam cracker includes a steam cracking unit to steam crack a feed stream to produce a stream comprising hydrogen, methane and C2+ hydrocarbons; a heat exchanger for cooling the steam cracking product stream; a separation unit for separating the cooled steam cracking product stream into a gas stream including hydrogen and methane and a liquid stream including methane and C2+ hydrocarbons, a demethanizer which is fed the liquid stream producing a third stream containing at least 95% methane and a fourth stream comprising C2+ hydrocarbons. The steam reformer includes a feed preheater which is fed the third stream and steam to provide a preheated stream and a steam reforming unit arranged for heating the preheated stream to at least 800° C. to steam reforming the heated stream and obtain a product stream containing hydrogen and CO2.