The modern world relies on a vast energy supply to fuel everything from transportation to communication, to security and health delivery systems. Perhaps most alarmingly, peak oil expert Michael Ruppert has claimed that for every calorie of food produced in the industrial world, ten calories of oil and gas energy are invested in the forms of fertilizer, pesticide, packaging, transportation, and running farm equipment. Energy plays an important role in the national security of any given country as a fuel to power the economic engine. Some sectors rely on energy more heavily than others; for example, the Department of Defense relies on petroleum for approximately 77% of its energy needs. Threats to energy security include the political instability of several energy producing countries, the manipulation of energy supplies, the competition over energy sources, attacks on supply infrastructure, as well as accidents, natural disasters, terrorism, and reliance on foreign countries for oil.