(CNN) -- U.S. gasoline prices have gone up about 4 cents per gallon in the past three weeks, but high unemployment is keeping downward pressure on prices, according to a new nationwide survey.
The latest Lundberg Survey, conducted Friday in 38 U.S. markets, found the average price of self-serve regular at $2.77 per gallon -- up 3.9 cents since the last survey, conducted July 23. But survey publisher Trilby Lundberg said the price of crude oil spiked and went down again during that period, indicating that prices are likely to drop again soon.
"Gasoline has not yet reacted to the crude oil drop of the past week," Lundberg told CNN. Meanwhile, she said, the supply of gasoline is "far more" than needed, "and our need is paltry."
"Gas demand growth has been arrested by unemplyment. It is flat so far this year," she said. And with unemployment at 9.5 percent, "All other factors pale in comparison to that."
The latest survey involved about 2,500 stations in the continental United States. The highest prices were found in San Francisco, where the average price was $3.21 per gallon; the lowest were in Jackson, Mississippi, at $2.54.
Average per-gallon prices in other cities:
Albuquerque, New Mexico: $2.80
Atlanta, Georgia: $2.69
Baltimore. Maryland: $2.68
Boston, Massachusetts: $2.74
Denver, Colorado: $2.66
Miami, Florida: $2.72
Portland, Oregon: $3.00
Tulsa, Oklahoma: $2.63