An apparatus for steam reforming of hydrocarbons comprises a heat exchange reformer having disposed within a plurality of vertical catalyst-filled tubes, through which a gas mixture comprising hydrocarbon and steam may be passed, and to which heat may be transferred by means of a heat exchange medium flowing around the external tube surfaces, wherein heat exchange adapting means are provided within the reformer so that the tubes have a zone of lower heat exchange extending from the bottom of the catalyst up to 25% of the catalyst depth with no heat exchange enhancement means provided in that zone. A process for steam reforming of hydrocarbons employs this apparatus.