A seasonal drop in consumption and lower crude oil prices contributed to a dip in prices at the gas pump over the past two weeks, an industry analyst said Sunday.

Between Nov. 5 and Friday, the average national price for all grades of gasoline dropped to $1.99, down 5 cents from the previous two weeks, said Trilby Lundberg (search), who publishes the semimonthly Lundberg Survey (search) of 7,000 gas stations across the country.

Prices for all grades have dropped nearly 8 cents over the past four weeks, she said.

The biggest seller, self-serve regular, had an average national price of $1.96 per gallon, down just over 5 cents. Mid-grade was $2.06 a gallon, down 5 cents, while premium was $2.16 per gallon, down 5 cents.

Of the cities surveyed, San Francisco led the nation in pump prices. The average price for a gallon of self-serve regular was $2.32. The best bargain was St. Louis, Mo., where the average price for self-serve regular was $1.67.

In California, the average price for self-serve regular dropped more than eight cents per gallon to about $2.29. The survey included an average of pump prices from Los Angeles, San Diego, San Francisco, Bakersfield, Fresno, Sacramento and Stockton.

Lundberg said gas prices have been declining because of lower crude oil prices and because of a traditional dip in gasoline consumption in the winter months.

"The short-term pump price prospects are for more declines," Lundberg said, adding that she doesn't expect the price of crude oil to increase in the near future.