A partial oxidation process for continuously producing synthesis gas, fuel gas or reducing gas in which process one fuel is replaced by a differing fuel without shutting down or depressurizing the gas generator. This multifuel process is not tied to one particular fuel and reacts slurries of solid carbonaceous fuel and/or liquid or gaseous hydrocarbonaceous fuels. Problems of fuel availability are reduced due to the wide selection of fuels that are suitable for the subject process. A two-section burner having a high turndown feature is employed that comprises a central conduit; a central bunch of tubes positioned in said central conduit; an outer conduit coaxial with said central conduit and forming an annular passage therewith; and an annular bunch of tubes positioned in said annular passage. The downstream ends of said central and/or annular bunches of tubes are respectively retracted upstream from the burner face a distance of about 0 to 12 i.e. 3 to 10 times the minimum diameter of the central exit orifie and the minimum width of the annular exit orifice. A control system is provided for switching the type of reactant fuel streams flowing through either one or both sections of the burner. The flow rates of the oxidant, fuel, and temperature moderator streams may also be varied in either one or both sections of the burner, thereby effecting a rapid turndown or turnup of the burner and a change in the production of the effluent gas.