The price of gas has declined recently, so much so that many experts think U.S. citizens may soon see prices fall under $3 for the first time in three years.

The average price for a gallon of gas in the U.S. fell 6.4 cents the last two weeks according to NBC News.

The latest Lundberg survey said the average price was 31 cents lower than a year ago, according to the Sept. 20 survey.

"It's normal for prices to fall in September," said Mark Jenkins, AAA spokesman, according to NBC News. "The summer driving season is over, demand is down, and refineries are switching to the cheaper winter-blend gasoline."

Results were determined based on 2,500 retail stations in 48 states.

Charleston, South Carolina had the cheapest gas at $3.14 per gallon according to the survey.

Drivers in San Francisco have to deal with the highest gas prices set at $4.01 per gallon.

"Prices could continue to fall another 5 to 10 cents before the end of the month," Jenkins said. "But it's unlikely."

GasBuddy's chief oil analyst Tom Kloza said that the fall will experience a "slow but steady attrition" in retail gas numbers, due to a record high U.S. refining rates and consumer demand.

"Supplies are adequate, and indeed gasoline now typically sells for just a few dollars more than raw crude costs," said Kloza, according to NBC News. "They'll go below $3.00 anytime soon."

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