PRODUCING SYNTHESIS GAS OR FUEL GAS WHEREIN THE FEEDSTOCK FOR A PARTIAL OXIDATION GAS GENERATOR COMPRISES A MIXTURE OF CARBONIFEROUS FUEL AND FROM ABOUT 1 TO 80 WT. PERCENT OF AN OXYGENATED HYDROCARBONACEOUS ORGANIC MATERIAL WHICH SUPPLIES THE FEEDSTOCK WITH A MINIMUM OF 0.5 WT. PERCENT OF COMBINED OXYGEN, AND THE PRODUCT GAS COMPRISES PRINCIPALLY CO AND H2 TOGETHER WITH MINOR AMOUNTS OF H2O, CO2, CH4, AND UNCONVERTED CARBON. BY REACTING ISOBUTYRALDEHYDE OR MOLASSES WITH HEAVY FUEL OIL OR VACUUM RESIDUUM THE CONCENTRATION OF CH4 IN THE PRODUCT GAS MAY BE INCREASED WHILE THE FREE OXYGEN CONSUMPTION AND THE REACTION TEMPERATURE AT A GIVEN LEVEL OF SOOT PRODUCTION AND STEAM/FUEL RATIO IS DECREASED.