A gas station with fuel prices in the $4 range in Los Angeles on April 11. With the price of gas above $3.50 a gallon in all but one state, there are signs that Americans are cutting back on driving, reversing a steady increase in demand for fuel as the economy improves. Reed Saxon/AP hide caption

itoggle caption Reed Saxon/AP

The ShopGirls, from Granite Falls High School in Granite Falls, Wash., prepare their car for the annual Shell Eco-marathon on Saturday at the George R. Brown Convention Center in Houston. Jeff Brady/NPR hide caption

itoggle caption Jeff Brady/NPR

In this photo provided by passenger Brenda Reese, an unidentified passenger takes photos with a cell phone of a hole in the cabin on a Southwest Airlines aircraft. Brenda Reese/AP hide caption

itoggle caption Brenda Reese/AP

In some parts of the country, like San Diego (above), gas prices are above $4 a gallon. Some Republicans are trying to tie those higher prices at the pump to President Obama's energy policies. Gregory Bull/AP hide caption

itoggle caption Gregory Bull/AP

Huge tanks help house the oil surplus in Cushing, Okla. Each tank holds more than 250,000 barrels of oil. Jeff Brady/NPR hide caption

itoggle caption Jeff Brady/NPR

Spent nuclear fuel rods are stored in pools of water at Japan's Fukushima Dai-ichi nuclear power plant. The water keeps the rods cool while protecting the environment from their radiation. Jiji Press/AFP/Getty Images hide caption

itoggle caption Jiji Press/AFP/Getty Images

Drivers in the middle of the country have gotten a break on gas prices because of bargain-priced oil coming in from Canada. Monika Wisniewska/iStockphoto.com hide caption

itoggle caption Monika Wisniewska/iStockphoto.com

A cargo ship transits the Suez Canal en route from the Mediterranean Sea to the Gulf of Suez at the city of Suez, Egypt, on Wednesday. Emilio Morenatti/AP hide caption

itoggle caption Emilio Morenatti/AP