Ryan Randazzo | The Republic | azcentral.com

A fuel crunch in the Phoenix area that has left many Circle K stations without gas has also pushed prices up about 46 cents per gallon in the past month. That's a bigger increase than national fuel prices have seen in the same time period.

The average price in metro Phoenix for a gallon of regular on Sunday was $2.93, according to AAA Arizona. That's up 18 cents from a week ago as prices have climbed a few cents a day.

Although prices are rising nationally as they normally do in the spring, the jump locally has been more pronounced, due to refinery-supply issues in California, according to one market analyst. The national average is only about $2.74, according to AAA, and has only gone up a few cents in the last week.

And Arizona's ubiquitous Circle K stations have struggled to keep gas available for three weeks now, with informal surveys by The Arizona Republic finding about one in five stations without fuel.

The company said this week it is working to address the problem but could not say when the supply crunch would be fixed. Fuel stations at Fry's Food Stores also have been affected.

Gas prices don't typically rise as fast as they have in the Phoenix area, AAA spokeswoman Michelle Donati said

AAA predicts continued increases as demand continues to increase going into the summer driving season, though they should be less pronounced than the past month.

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"What we are experiencing right now, part of it is seasonal, part is unforeseen circumstances, and the price surge is above what we normally see this time of year," she said.

What's going on with the fuel supply?

Circle K has said that it's run out of gas at some Arizona stations because of a "perfect storm" of problems with its own pipeline, refinery outages and ethanol distribution.

Problems with the national ethanol market have been well-documented in the past month. Ethanol is a fuel additive usually made from corn. Storms in the Midwest have disrupted that market by shutting down some ethanol plants and the railroads serving them.

Patrick DeHaan, an analyst with GasBuddy.com in Chicago, said the larger Phoenix supply is suffering because of refiner issues in California.

Cheryl Evans/The Republic

"Refineries in Southern California in recent weeks have been bogged and dogged by problems," he said. "All of these have culminated to supply crunch. That has pushed up gas prices as a result."

The Phoenix area is required to use a particular fuel blend known as CBG, or "cleaner burning gasoline," while rural Arizona areas don't have the same requirement. The supply crunch affecting Phoenix could be tied to the blending of that fuel, DeHaan said.

"The supply of CBG is tight, but the ethanol blended into that CBG is tight as well," he said.

Refineries will sell both "branded" gasoline produced for a particular company, as well as less-expensive "unbranded" or generic fuel, he said. The supply crunch in the Phoenix area is apparent by current prices for unbranded fuel, which is selling for about 30 cents more per gallon on the wholesale market.

"We call that an inverted rack, and that almost always highlights a supply disruption or challenge," he said. "At the retail level, prices are soaring because of the supply challenge."

DeHaan said he did not know any particulars of Circle K's fuel contracts, but he suspects that the refiner that supplies Circle K is either not allocating enough fuel to meet the company's current demand, or that the company is strategically allowing some stations to go dry.

They might be doing this, he said, to avoid paying the higher wholesale prices today, which could come crashing down overnight once refiners get back online.

"A lot of stations don’t want to play this high-stakes game where they fill up today but in a couple days it is selling 30 cents less," he said.

Arizona gas facts

What's the most gas has ever cost nationally? The national average for a gallon of regular hit $4.11 on July 17, 2008, according to AAA.

What is the highest price ever in Arizona? The state average price hit $4.09 for a gallon of regular on July 3, 2008.

How much fuel is sold in Arizona? Arizonans buy about 8.1 million gallons of gasoline per day. In Maricopa County, about 4.8 million gallons are sold daily.

Where does Phoenix get its gas? Kinder Morgan runs two pipelines into the Phoenix area. One comes from California and through the Yuma area. The other comes from El Paso, Texas, through the Tucson area.