A method for gasifying carbonaceous materials to fuel gases comprises the formation of an ultra-superheated steam (USS) composition substantially containing water vapor, carbon dioxide and highly reactive free radicals thereof, at a temperature of about 2400.degree. F. (1316.degree. C.) to about 5000.degree. F. (2760.degree. C.). The USS composition comprising a high temperature clear, colorless flame is contacted with a carbonaceous material for rapid gasification/reforming thereof. The need for significant superstoichiometric steam addition for temperature control. Methods for controlling a gasification/reforming system to enhance efficiency are described. A USS burner for a fluidized bed gasification/reforming reactor, and methods of construction, are described.