Enjoy that road trip! July 4th gas hasn't been this cheap in years

Four factors that determine gas prices
Four factors that determine gas prices

Drivers are enjoying the cheapest Fourth of July gasoline in more than a decade. Enjoy it while it lasts: Experts say prices will start inching higher soon.

The average price nationwide for a gallon of regular is $2.23, down 15 cents from a month ago, according to AAA.

And really cheap gas is even more common than suggested by that average: About 25% of gas stations nationwide are selling gas for $2 a gallon or less.

The last time gas was this cheap heading into Independence Day was 2005.

But wholesale gasoline prices have already started to climb up, and that will probably translate into modestly higher prices at the pump in coming days, said Tom Kloza, chief oil analyst for the Oil Price Information Service, which tracks gas prices for AAA.

"I think today's number might be about as low as it gets this summer," Kloza told CNNMoney.

The price of crude oil has started to creep up as U.S. oil production has declined recently, he said. But demand will stay strong. "From now to Labor Day, there's no question we'll use plenty of fuel," Kloza said.

Those factors should combine to send prices up about 10 cents a gallon, Kloza said. The price will probably then drop again come fall, when gas stations stop selling the more expensive blend of gasoline required during the summer months to fight smog.

Related: Have oil prices stopped plunging?

Meanwhile, Indiana, Montana, South Carolina, Tennessee and West Virginia raised state gasoline taxes on July 1.

South Carolina still has the cheapest average gas price in the country at $1.90 a gallon, despite a two-cent increase in gas taxes.

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