Synthesis gas, reducing gas, or fuel gas is produced by the partial oxidation of ash-containing solid carbonaceous and/or liquid hydrocarbonaceous fuel at an autogenous temperature in the range of about 20.degree. F. to 200.degree. F. below the softening temperature of the ash in said fuel, and at a pressure in the range of about 17 to 100 atmospheres to produce a raw effluent gas stream containing entrained carbon-rich fly-ash which is separated from the effuent gas stream. A fuel mixture comprising about 20 to 100 wt. % of said carbon-rich fly-ash and about 0 to 80 wt. % of a supplemental fuel is reacted by partial oxidation at an autogenous temperature of about 100.degree. F. above the ash-fusion temperature, and at a reduced pressure e.g. in the range of about 1 to 16 atmospheres and at least 16 atmospheres below the pressure in the partial oxidation reaction used to produce said carbon-rich fly-ash. By reducing the pressure less carbon-rich particulate material is produced in the second partial oxidation reaction at a significant cost savings and improved process efficiency.