Process and apparatus for the preparation of synthesis gas by catalytic steam and/or CO.sub.2 reforming of a hydrocarbon feedstock comprising the following steps: (a) heating the reaction mixture of hydrocarbon feedstock and steam and/or CO.sub.2 in the flue gas containing waste heat section from the fired tubular reformer (b) adiabatic reforming of the reaction mixture outside the waste heat section by contact with a solid reforming catalyst (c) repeating steps (a) and (b) until the desired reaction mixture composition and temperature is reached (d) feeding the reaction mixture to the fired tubular reformer and further reforming the mixture to the desired composition and temperature, wherein the adiabatic reforming of the reaction mixture is conducted in the process gas piping system in the flue gas-containing waste heat section, the piping system having adiabatic zones outside the heating section and containing solid reforming catalysts comprising one or more catalyzed structured elements.