Sludge gas is a valuable commodity when the best possible use for it can be found. When a new plant is designed or an old plant that includes anaerobic digestion is modified, the decision made on sludge gas utilization will have a significant economic impact. Once cogeneration is chosen as the best alternative for a plant, other decisions must be made. This paper outlines some of the decisions made during the design of the Eureka, California, wastewater treatment plant cogeneration system.