ATLANTA (CNN) - Gas prices fell another 3 cents over the past two weeks, to an average of $2.21 per gallon of self-serve regular, a national survey said Sunday.

That makes a total drop of 7.5 cents during the past month, said Trilby Lundberg, publisher of the Lundberg Survey, which tallies prices at about 7,000 gas stations nationwide every two or three weeks.

"The reason that prices are moderating is that both crude oil and gasoline supplies are enhanced," Lundberg told CNN in a telephone interview.

The downward trend reverses a 50-cent increase in prices at the pump that started at the beginning of the year and ended in a survey carried out April 8.

"Probably more price cuts at the pump are on the way, unless there is a reversal in the improved supplies of either crude oil or gasoline," she said.

San Francisco had the nation's highest prices, at $2.60 per gallon of self-serve regular. At 58 cents per gallon, the Bay Area city has some of the nation's highest taxes on gas.

The lowest prices were in Minneapolis, where drivers paid an average of $1.95 per gallon, Lundberg said.

Here are some other prices for a gallon of self-serve regular:

Atlanta: $2.08

Dallas: $2.14

Denver: $2.14

Chicago: $2.27

Hartford, Conn.: $2.29

Las Vegas: $2.43

Reno: $2.53

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(Enough about gas ... how about food challenges?)