As warm weather puts vacationers behind the wheel, experts see a further run-up in gasoline prices. It's unclear whether the price will average $4 per gallon, but it has already surpassed that in California, where gas taxes are high, and Hawaii, where the price includes costs of transporting the fuel.

In the Seattle-Bellevue-Everett area, regular unleaded gasoline is going for $3.48 a gallon, AAA reports.

"It's going to be another drag down on the economy," says Peter Morici, a professor at the University of Maryland School of Business and former chief economist at the U.S. International Trade Commission. "As it is, people feel poorer because their houses are falling in value, interest rates are higher on their credit cards and they can't borrow any more money on their homes."

Morici says it's a "distinct possibility" that prices could hit $4, though he sees $3.50 as more likely. A March 11 report from the U.S. Energy Department's Energy Information Administration projects a peak near $3.50 this spring.

Higher prices and a weakening economy have resulted in flat gas demand so far this year compared with last, says AAA fuel-price analyst Geoff Sundstrom. Typically, demand grows at a 2 to 3 percent rate. "We're definitely seeing weakness on the part of the American consumer in terms of gas consumption and miles driven," he says.