(CNN) -- Gasoline prices plunged more than 21 cents a gallon over the past two weeks to a national average of $2.66 amid an abundant supply of fuel at service stations, a national survey said Sunday.

Lower demand for gas with the end of the summer driving season and a drop in crude oil prices combined to send prices downward across the United States, according to Trilby Lundberg, publisher of the "Lundberg Survey."

Lundberg, whose survey tallies prices every two to three weeks at about 5,000 gas stations in all 50 states, said gas prices were "punctured."

The average price of a gallon of gas has fallen nearly 37 cents a gallon in the last four weeks, according to the Lundberg Survey taken on Sept. 8.

The drop means prices are 35 cents lower than a year ago in the days following Hurricane Katrina, which disrupted of the oil industry along the Gulf coast.

"The situation has reversed itself," Lundberg said. "Rather than a shortage of gasoline hiking prices, we've had more than enough gasoline."

"Most of the impetus for the retail gas puncture has been spent," she added. "Unless crude oil prices lose several more dollars per barrel, which is not very likely, then further retail gas prices cuts will be slower from here."

OPEC oil ministers meet in Vienna on Monday and are not expected to change production levels among member countries, Lundberg said.

Drivers in Des Moines paid the least, at $2.32 per gallon; drivers in Honolulu the most, at $3.17. Los Angeles and Chicago led the Lower 48, at $2.96.

The following are prices in other U.S. cities:

Tulsa, Okla.: $2.34

Cleveland: $2.37

Atlanta: $2.48

Houston: $2.49

Phoenix: $2.57

Boston: $2.68

Denver: $2.87

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