ATLANTA (CNN) - Gas prices shot up nearly 25 cents per gallon over the past two weeks, to a national average of $2.91 for self-serve regular, a survey said Sunday.

"Gasoline is riding crude oil's price surge," said Trilby Lundberg, whose Lundberg Survey tallied prices at about 7,000 gas stations on April 7 and again on April 21.

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During that interval, the price of crude oil rose $8, closing Friday at $75.17 per barrel on the Nymex, about $5 more than its peak price last summer, when hurricanes in the Gulf damaged a number of refineries.

The report pretty much matches the daily survey of 60,000 service stations conducted for the motorist group AAA, which said the average price of self-serve regular reached $2.90 Sunday. (Click here for full story)

Drivers in San Diego paid the most, at an average of $3.12 per gallon of self-serve regular; drivers in Boise, Idaho paid the least, at an average of $2.54 per gallon, she said.

The District of Columbia and five states saw average prices of $3 or higher, she said. The states are Illinois, Nevada, Wisconsin, California and Hawaii.

Lundberg blamed some of the price rise on the costs of blending ethanol into gasoline and delivering the final product. Government mandates require that a certain amount of ethanol be blended into gasoline, and gasoline containing ethanol cannot be shipped via pipeline, driving up the cost of delivery.

Further upward pressure on prices comes from ethanol import barriers - the United States has imposed a 54-cent-per-gallon tariff on imported ethanol, Lundberg said.

"Lifting that tariff could help contain gasoline prices, but of course that would take time and a great deal of political movement," she said.

Refiners and distributors are scrambling to get domestic supplies of ethanol, which are tight, she said. That shortage has resulted in spotty outages of gasoline in Texas and several Eastern markets, including Virginia and Pennsylvania, she said.

Upward pressure on the price of oil is also coming from Nigeria, where 25 percent of production is out, the result of rebel attacks on oil facilities, she said.

Uncertainty over what will happen in Iran is also adding to the price of oil, she said.

Iran has said it is pursuing nuclear enrichment for peaceful purposes, a move that has distressed many in the international community, including the United States, which contends that Iran's goal is to develop nuclear weapons.

Still, relief may be in sight. Kuwait has offered to release 2 million barrels of oil per day if the Organization of Petroleum Exporting Countries (OPEC) agrees, Lundberg said.

And prices are not at a record when inflation is considered. In February 1981, the crude oil price was nearly $17 higher -- just under $92 per barrel,

in today's dollars -- if inflation is factored in, Lundberg said.

Gasoline has about 15 cents to go to meet its inflation-adjusted record high of $3.03, also set in February 1981, when the Iranian revolution and oil embargoes caused world petroleum prices to surge.

Here are prices in some other areas: Long Island, N.Y.: $3.10; Los Angeles: $3.06; Milwaukee: $3.04; Chicago: $3.00; Hartford, Conn.: $2.97; Dallas: $2.97;Philadelphia: $2.93; Birmingham, Ala.: $2.85; Denver: $2.78; Atlanta: $2.90.

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