(CNN) -- Gas prices continued their downward spiral across the nation, falling by an average of nearly 8 cents a gallon over the past two weeks, the publisher of the national Lundberg Survey said Sunday.

The average price of self-serve regular gasoline is $2.20, according to the survey taken of more than 7,000 U.S. filling stations between Oct. 6-20, Trilby Lundberg told CNN.

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Prices at the pump have dropped more than $.82 since Aug. 11, she said.

The price drop "is due to another sizable dip" in the price of crude oil, Lundberg said, which fell despite a decision made Friday by the Organization of the Petroleum Exporting Countries (OPEC) to cut production by 1.2 million barrels a day.

"The market is doubtful that (OPEC) will cut that much and that's why on the actual day of the decision, crude price fell again this past Friday by $1.68," Lundberg explained.

Gasoline prices have been closely watched, and they will get even more scrutiny this week as the no. 1 U.S. oil company Exxon Mobil (Charts) is expected to report earnings Thursday. Shares of exxon edged lower Friday after OPEC's announcement.

Stocks of other oil majors BP (Charts),ConocoPhillips (Charts), Chevron (Charts) and Royal Dutch Shell (Charts) also edged lower Friday.

For the latest survey period, Tulsa, Okla., had the lowest average price for a gallon of gasoline at $1.98.

The most expensive gas was in Honolulu at $2.84 a gallon.

Here is a sampling of other cities:

Atlanta $2.05

Austin, Texas $2.16

Chicago $2.34

Dallas $2.05

Denver $2.18

Long Island, N.Y. $2.27

Sacramento $2.34

Seattle $2.46

The axis of diesel