Gasoline prices: up, and rising

(CNN) -- Gas prices rose more than eight cents in the past two weeks to a national average of $2.87 per gallon of self-serve regular -- and are expected to further rise -- according to a national survey released on Sunday.

That marks a rise of 69 cents at the pump since late January, Trilby Lundberg, publisher of "Lundberg Survey," said. The "Lundberg Survey" tallies gas prices every two to three weeks at about 5,000 gas stations.

The latest survey was conducted Friday.

The current price is about four cents lower than a year ago, Lundberg said, and it is about 15 cents less than the all-time peak in August.

Lundberg attributed the slight rise in gas prices to the current prices of refinery repairs, which are "keeping the market tight," she said.

Several refineries have had recent problems. Valero Energy Corp. shut its refinery in McKee, Texas, after a fire on Feb. 16, and company officials did not expect full resumption until late in the year. And earlier this month, the western hemisphere's second-largest refinery -- the Hovensa Refinery on the island of St. Croix, the Virgin Islands -- shut for 10 days of maintenance, Lundberg had told CNN earlier.

Lundberg said gas prices are expected to peak and then fall over the next few days, as refining operations return to normal, and as the influx of gasoline imports continue to bolster the gasoline supply in the United States.

Some areas of the country are already experiencing a decline in gas prices, Lundberg said.

"Certain wholesale gas prices plunging in some parts of the country," she said. By early May, a decline of five or 10 cents could be possible nationwide.

However, she warned that any new scare in the crude oil industry, which is skittish about Nigeria's political situation and Iran, could send gas prices back up.

Gas prices affect the incomes of such companies as BP (Charts), Exxon Mobil (Charts, Fortune 500), Chevron (Charts, Fortune 500) and ConocoPhillips (Charts, Fortune 500).

Drivers in Minneapolis, paid the least at $2.65 per gallon of self-serve regular, according to the survey, and drivers in San Francisco paid the most at $3.37.

Here are some other prices:

Jackson, Miss.: $2.69

Atlanta: $2.76

Denver: $2.77

Boston: $2.78

Dallas: $2.79

Las Vegas: $3.02

Chicago: $3.02

Seattle: $3.13

Los Angeles: $3.28

Washington, D.C.: $2.96