(CNN) -- Gas prices rose 6.5 cents over the past two weeks to $2.81 per gallon of self-serve regular, the first increase at the pump since early July, a national survey said Sunday.
"It's crude oil at work," said Trilby Lundberg, publisher of the Lundberg Survey. She noted that, from Aug. 24 to Sept. 7, the price of crude rose by more than 13 cents per gallon, outpacing the rise at the pump by two to one.
The survey of prices at about 5,000 stations found Chicago drivers paid the most on average ($3.27 per gallon) and drivers in Newark, N.J., the least ($2.52 per gallon).
Prices are not likely to drop soon, she said. OPEC's meeting this Tuesday in Vienna does not include plans to hike production, and five of the cartel's 12 members - Iran, Iraq, Nigeria, Venezuela and Algeria - are embroiled in "disturbing news headlines," she said.
In Algeria last week, dozens of people were killed in two suicide attacks, one of them in an apparent attempt to assassinate the country's president. A militant Islamic group that recently renamed itself Al Qaeda Islamic Maghreb has claimed responsibility for the attacks, according to a statement posted on the group's Web site Sunday.
Still, Lundberg predicted retail prices will be relatively stable in coming weeks "unless oil prices surge further."
Refining capacity will drop slightly in coming weeks as the industry switches from more expensive spring and summer gas formulations to those of fall and winter. In addition, some capacity will be diverted to production of heating oil.
Here are average prices in some other cities:
Atlanta: $2.74
Boise, Idaho: $2.73
Dallas: $2.62
Hartford, Conn.: $2.88
Long Island, N.Y.: $2.86
San Francisco: $2.92
Washington, D.C.: $2.72 
