The national average for self-serve, regular unleaded gas was $4 per gallon on May 6, up 11.98 cents from April 22, according to the nationwide Lundberg Survey.

This was still below the all-time high of $4.11 on July, 11, 2008, and last week's fall in crude oil prices may lead to a 8- to 12-cent drop in prices at the pump over the next few weeks, according to Trilby Lundberg, the survey's editor.

"If the current oil price stays, gas prices will slide," Lundberg said, adding that gas prices had peaked around May 4, prior to a $12.06 drop in crude oil prices between May 4 and May 6.

There is already some evidence that gas prices are on a downward trend. In the wholesale market, which is made up of retailers and commercial buyers, prices are already dropping. Unbranded gasoline is down 21 cents per gallon, while branded gasoline is down 14 cents per gallon since Monday, May 2, Lundberg said.

Still, there is no guarantee that crude oil prices will not bounce back and a number of risks remain. Libya's oil production has not been restored and, while U.S. gas demand is slipping because of the higher prices, it is not clear whether it is affecting developing countries' demands for energy.

"We can't know what oil prices will do," said Lundberg. "The main drivers of oil price increases have not gone away."

At $4.50 per gallon, Chicago had the highest average for self-serve, regular unleaded gas, while the lowest price was $3.62 in Tucson, Arizona.