Process and system for the production of synthesis gas from a hydrocarbon feed stock comprising the steps of endothermic and/or adiabatic catalytic steam reforming and autothermal steam reforming in series, wherein the steam reforming is carried out in one or more endothermic stages in series or in one or more adiabatic steam reforming stages in series with intermediate heating of feed stock gas leaving the adiabatic reforming stages and wherein carbon monoxide containing gas characterised by having a molar ratio of hydrogen to carbon of less than 4.5 is added prior to at least one of the endothermic or adiabatic steam reforming stages and/or prior to the autothermal steam reforming step.