Drivers who haven’t filled up their cars since last week are in for a pleasant surprise at the pump, though it may be short-lived.

The average price for a gallon of gas in South Carolina dropped 12 cents in the past week — the sharpest one-week decline in the price of gas in four years, according to AAA Carolinas. Still, the average in South Carolina is 11 cents above the average a year ago and will rise again as temperatures drop.

Prices usually drop this time of year after the summer driving season. The drop likely was bigger this year because of a strong dollar against the euro and the calming of conflicts in oil-producing countries such as Iraq and Libya, the Charlotte-based motor club said.

“The price drop is great news for drivers,” said chief executive David Parsons. “However, the nature of gas pricing today mostly depends upon issues outside the U.S., like armed conflicts in oil-producing nations, the dollar’s value against the euro and the demand for oil in developing countries like China, India and Brazil.”

The average price for a gallon of gas in South Carolina was $3.36 Wednesday, compared with $3.48 a week ago, according to AAA Carolinas. The price of a gallon has dropped 27 cents since mid-September.

In Myrtle Beach the average Wednesday was $3.32, while in the Greenville-Spartanburg area the lowest average price was $3.30 a gallon. Charleston was the highest at $3.48.

The average gas price in North Carolina on Wednesday was 11 cents less than seven days ago, also marking the greatest price decline in one week since 2008, according to AAA Carolinas. The average price for a gallon of gas there was $3.58, compared to $3.69 one week ago.

However, once temperatures start to drop, look for prices to rise as refineries switch from gasoline to heating oil.

“This is like a little window,” AAA spokesman Tom Crosby said. “As the winter goes along … that will cause our gasoline prices to go up.”

When the dollar is strong against the euro, speculation in oil futures diminishes and crude oil becomes cheaper, Crosby said. He expects that gas prices will continue to drop between now and Thanksgiving, typically the most heavily traveled four-day holiday and often a time when prices stabilize or rise slightly.

However, the threat of a hurricane in the Gulf of Mexico, escalating geopolitical tensions in the Middle East or other events that could threaten supply would also cause prices to rise, Crosby said.

“But right now demand is down and the dollar has gotten a lot stronger,” he said.