A process and plant for producing a synthesis gas chiefly consisting of hydrogen and carbon monoxide by catalytic steam reformation of a hydrocarbonaceous feed gas, wherein the heat of burners required for the chemical reforming reactions to take place is generated by producing a flue gas and wherein, by utilizing the heat contained in the synthesis gas and in the flue gas, a pure steam is generated from boiler feed water and a process steam is generated from process condensate, wherein for the generation of the pure steam synthesis gas and flue gas are used and for the generation of the process steam a part of the pure steam is used as heat-transfer medium and the remaining part of the pure steam is discharged from the process as export steam.