U.S. average retail gasoline prices fell slightly during the past two weeks as demand remained flat, but could rise in coming weeks and months if the price of crude oil stays above $70 per barrel, according to the latest nationwide Lundberg survey.

The national average price for self-serve regular unleaded gas was $2.8879 a gallon on June 23, a decline of about 4.5 cents per gallon in the past two weeks, according to the survey of about 7,000 gas stations.

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The price on June 23 was a drop of 6 cents from the year's peak price of $2.9473 per gallon on May 5, the survey said. That price was the crest of a 73-cent rise since late December 2005, it said.

"At current prices, demand is not growing, (but) it's not shrinking either," said survey author Trilby Lundberg in an interview.

At $3.26 a gallon, Honolulu, Hawaii had the highest average price for self-serve regular gas, while the lowest price was $2.61 a gallon in Charleston, South Carolina, the survey said. The highest price on the 48 continental states was San Diego, California, at $3.16, the survey said.

Gasoline prices could rise if crude oil prices surge or demand for ethanol used as a gasoline additive rises, she said.

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