Abstract: An improved anaerobic digestion process is provided to enhance the methane content of product gas so that no further processing may be required for utilization as high quality, high Btu gas comprising greater than 90 percent methane. Operating conditions of lowered carbon dioxide influent concentration to the methane production digester and operation of the methane production digester under pressurization achieve high conversion efficiency rates and high methane content product gas. The carbon dioxide produced during the anaerobic digestion may be physically and chemically separated and removed thereby reducing the carbon dioxide content of the product gas.