Abstract: Improved heat utilization is achieved in a process for the catalytic steam reforming of hydrocarbons to form a product stream rich in hydrogen by (a) first passing the process gas through a first portion of catalyst comprising 25-75% of the total steam reforming catalyst (whereby the heat needed for the endothermic reactions during reforming and for heating the process gas is supplied partly from a moderately hot flue gas generated by combustion of a fluid fuel and partly from the product stream) and then (b) passing the partly reformed process gas through the remaining portion of the reforming catalyst. In this second step, the heat needed for the further endothermic reactions and for heating the process gas is supplied by a hot flue gas, the hot flue gas thereby being cooled to form the moderately hot flue gas mentioned unde (a). A reactor for use in this process is also described.