The U.S. armed forces consume enormous quantities of fuel (diesel, jet fuel, gasoline, heating oil and etc). Last year, the Department of Defense spent about $90 on fuel, each week, for each active duty member of the armed forces. It's the single largest expense for "expendable" items in the military. Last year, the Department of Defense bought $7.4 billion worth of petroleum based fuel. That's a 57 percent increase from 2004. This increase was caused by greater consumption, and rising prices. When it comes to shipping (largely by ship) stuff to the troops overseas, most of that material is fuel.
Over half the fuel is consumed by the U.S. Air Force, and because of that it is under pressure to either retire B-52s and C-5s (which have older, gas guzzling, engines), or replace their engines with more fuel efficient models. Oddly enough, even their current engines, B-52s are still much cheaper to operate than the more recent B-1B and B-2 bombers.