In 1944 General George S. Patton's Third Army was racing across southern France. In his haste to be the first U.S. commander to cross into Germany, however, Patton overextended his supply lines. His armored columns ground to a dead stop. Faced the choice of waiting until he could be resupplied or draining the fuel of captured German vehicles, Patton chose the latter. His tanks and armored personnel carriers continued to steamroll toward Germany, powered by the German's own ersatz gasoline – synthetic fuel manufactured from coal.
This makes me not worry so much that gasoline engines will become obsolete after peak oil production in 2006.