Abstract: An improved method and apparatus for treating a biodegradable organic material in an aqueous medium to produce methane gas is disclosed. The method involves flowing the aqueous medium under pressure through a hydrolytic-redox, immobilized microbe bioreactor to form a reaction product and then continuing the flow of the reaction product through an anaerobic, immobilized microbe bioreactor whereby methane gas is evolved. The aqueous medium is flowed in a downward direction counter to the flow of the gaseous carbon dioxide given off during the reaction and the aqueous medium may be recycled.