ATLANTA (CNN) -- Prices at the pump are up nearly 9 cents in the past two weeks and a total of 18 cents in the past month, but the increase is likely to slow, according to a survey published Sunday.
The national average for a gallon of self-serve regular is $2.81, the Lundberg Survey found in the survey conducted Friday.
That's an increase of 8.6 cents since the last survey two weeks ago, and a total increase of 18.2 cents in the past month.
However, the rise is not expected to continue over the next few weeks, said publisher Trilby Lundberg -- mainly because there is a glut of crude oil and gasoline, while demand remains relatively flat and is forecast to remain so because of economic conditions.
"Supply, barring an emergency somewhere in the world, is not going to be tight," Lundberg said.
Worldwide, the demand for crude oil weakens in the summer months because warmer weather decreases the need for heating oil, she said.
While demand for gasoline typically increases in the summer months in the United States, the struggling economy and high unemployment rates probably will dampen that demand, she said.
And Lundberg said she doesn't expect the Organization of the Petroleum Exporting Countries (OPEC) to stop overproducing -- "not at these prices." So while prices may rise a few more pennies, the increase is predicted to slow, she said.
The current average price is 86 cents above the price of a gallon of self-serve a year ago, Lundberg said. The survey tallies prices at thousands of gas stations nationwide.
The city with the lowest average price in the latest survey was Newark, New Jersey, at $2.60. The highest was Honolulu, Hawaii, at $3.38.
Here are average prices in other cities: