The Department of Defense is the largest single consumer of energy in the United States. Petroleum-based fuels are by far the dominant source. Each year, DoD uses more than 100 million barrels of fuel for its aircraft, ships, and ground tactical vehicles. Fuel is critical to the military’s ongoing operations. The costs, availability, logistics, and greenhouse gasses associated with petroleum-based fuels, however, represent a significant risk to DoD and national security.