Abstract: An improved method and apparatus for feeding a crushed or pulverized solid supply material such as coal or the like, from a supply source under ambient pressure into a reactor or the like which is under significantly higher pressure; such as in connection with a hydrogenation/oxidation process producing so-called "fuel" or "synthesis" gases. A liquefied gas such as carbon dioxide or the like, is fed under pressure into a moving supply of such materials (as may be contained in a closed casing screw conveyor/extruder or the like) in order to form a slurry which is suitable to be pumped into the receiver against its superior pressure. Process temperatures are so controlled that as the input liquefied gas component of the slurry migrates toward the lower pressure feed inlet end of the conveyor in response to the superior pressure at the discharge end of the conveyor, it solidifies into solid particles which intermingle with and substantially fill the interstices between the supply material particles.