Vastly increased demand for oil in rapidly modernizing China and India, warfare and instability in the Middle East and the weakening U.S. dollar have revived fears of a new energy crisis. Gasoline shortages — and the accompanying lines at gas stations — were thought to have ended with the Jimmy Carter administration. But as 2008 began, American drivers were paying more than $3 a gallon, and crude oil hit a milestone — $100 a barrel. Some oil experts warn of even bigger price shocks to come as oil-producing nations use more and more of their own oil, and energy demand jumps 50 percent by 2030. Some experts predict an oil "production crunch" within four to five years that will have severe geopolitical and economic impacts, and one expert says the energy supply-demand gap could create "social chaos and war" by 2020. In any event, the days of cheap, plentiful oil appear to be over, and motorists may have to learn how to conserve energy.