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

President Obama hugs NASA astronaut Mark Kelly, husband of Rep. Gabrielle Giffords, during a ceremony last week in Tucson, Ariz. Jewel Samad/AFP/Getty Images hide caption

itoggle caption Jewel Samad/AFP/Getty Images

Emergency personnel work on Jan 8 at the scene where Rep. Gabrielle Giffords, (D-AZ) and others were shot outside a Safeway grocery store in Tucson, Ariz. Nearly anyone at the scene that day will be at risk for post traumatic stress disorder, but it's difficult to predict who will be affected. Matt York/AP hide caption

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Pronghorn antelope cross a rural Wyoming road south of Rock Springs, near a Bureau of Land Management lease sale challenged by the Wyoming Wildlife Federation. Jeff Brady/NPR hide caption

itoggle caption Jeff Brady/NPR