A system for producing syngas containing at least hydrogen and carbon monoxide, comprising: a partial oxidation reactor that exothermically reacts a first portion of a hydrocarbon feed stream with an oxidant gas comprising molecular oxygen and optionally steam and carbon dioxide in a first reactor to produce an exothermically-generated syngas product, wherein the feed stream includes methane; a gas heated reformer positioned adjacent to the POX that endothermically reforms a second portion of the hydrocarbon feed stream with steam and optionally carbon dioxide over a catalyst in a heat exchange reformer to produce an endothermically-reformed syngas product, wherein heat used in generation of the endothermically-reformed syngas product is derived from heat released by cooling the combined stream of the product syngas from the POX and the GHR; a mixing zone disposed between the tubes of the GHR and the POX stage wherein the gases from the POX stage and the GHR stage are mixed; and a waste heat boiler positioned adjacent to the GHR which generates steam using heat derived by cooling the combined syngas stream from the GHR; and wherein the POX, GHR and the WHB are contained in a single pressure vessel independent of piping between the POX, the GHR, and the WHB and having internal mixing between syngas from the POX and syngas from the GHR to produce a combined syngas stream that flows over tubes of the GHR providing heat for endothermic reforming reactions and passing combined syngas streams to exit a shell side of the GHR and enter the WHB to provide heat for production of steam, characterized in that an internal arrangement of the GHR includes a tube sheet which includes an opening through which a total syngas flow can pass isolated from a total GHR feed stream through a cover secured to and covering a part of the tube sheet in which the GHR tubes are secured. a partial oxidation reactor that exothermically reacts a first portion of a hydrocarbon feed stream with an oxidant gas comprising molecular oxygen and optionally steam and carbon dioxide in a first reactor to produce an exothermically-generated syngas product, wherein the feed stream includes methane; a gas heated reformer positioned adjacent to the POX that endothermically reforms a second portion of the hydrocarbon feed stream with steam and optionally carbon dioxide over a catalyst in a heat exchange reformer to produce an endothermically-reformed syngas product, wherein heat used in generation of the endothermically-reformed syngas product is derived from heat released by cooling the combined stream of the product syngas from the POX and the GHR; a mixing zone disposed between the tubes of the GHR and the POX stage wherein the gases from the POX stage and the GHR stage are mixed; and a waste heat boiler positioned adjacent to the GHR which generates steam using heat derived by cooling the combined syngas stream from the GHR; and wherein the POX, GHR and the WHB are contained in a single pressure vessel independent of piping between the POX, the GHR, and the WHB and having internal mixing between syngas from the POX and syngas from the GHR to produce a combined syngas stream that flows over tubes of the GHR providing heat for endothermic reforming reactions and passing combined syngas streams to exit a shell side of the GHR and enter the WHB to provide heat for production of steam, characterized in that an internal arrangement of the GHR includes a tube sheet which includes an opening through which a total syngas flow can pass isolated from a total GHR feed stream through a cover secured to and covering a part of the tube sheet in which the GHR tubes are secured.