(CNN) -- With Thanksgiving on the horizon, U.S. gas prices are up nearly a nickel to the highest price since early May, according to a new survey of filling stations.
The latest Lundberg Survey of cities in the continental United States was conducted Friday. It showed the national average for a price of self-serve unleaded gasoline at $2.87, an increase of 4.5 cents from the last survey two weeks earlier, survey publisher Trilby Lundberg said.
That's the highest price since May 7, when the national average per gallon was $2.92, Lundberg said. However, this price hike may be the last for the near future, as oil prices have declined in recent days to about the same level as a month ago, she said.
The main factor in the decline is likely negative views about oil demand because of economic conditions. For example, investors in Asia and Europe carry "a certain gloom about demand" when they hit the trading floor, she said. In addition, a weakened euro has made the dollar appear stronger, which also cut into the oil price a bit, she said.
Assuming oil prices don't "jump wildly either down or up in the next few days," the gasoline price is about 23 cents above the price on November 20, 2009, she said -- a sizable amount to be paying at the pump, since many Americans have not seen better economic conditions.
"Twenty-three cents, it may not sound like a whole lot," Lundberg said. "But for many American motorists, it is enough to pinch."
The Lundberg Survey sampled prices at about 2,500 gas stations. The highest average price in the continental United States was in San Francisco, California, at $3.20 per gallon. The lowest price was iin Denver, Colorado, at $2.63.
Average per-gallon prices in other cities:
Baton Rouge, Louisiana: $2.70
Atlanta, Georgia: $2.81
Miami, Florida: $2.88
Las Vegas, Nevada: $2.89
Boston, Massachusetts: $2.97
Seattle, Washington: $3.09
Tulsa, Oklahoma: $2.72
Chicago, Illinois: $3.09
Los Angeles, California: $3.11
Houston, Texas: $2.67