Abstract: A methanation reactor to be used preferably in an integrated urea-ammonia process for methanizing carbon oxides is disclosed in which the catalyst bed and an underlying heat exchanger of the tube-bundle type make up a unit mounted centrally of the reactor casing with a gap left between the reactor casing inside wall and centrally mounted unit. Fresh gases to be methanized enter the gap, then into the heat exchanger from below and flow upwards to the catalyst bed and thereafter flow down to the exchanger again. Incoming gases sweep the exchanger tubes from the outside, while the reacted gases flow in the interior of the tubes of the exchanging boundle. Particular blanket and a gland-seal system is provided to minimize the escape of gaseous fluids from the reactor.