(CNN) -- Average U.S. gas prices edged up a fraction of a penny over the past two weeks, buoyed by a sharp increase in California as other parts of the country saw declines, according to a survey released Sunday.
The average price of a gallon of regular gasoline went up about 0.37 cents between September 21 and October 5, according to the Lundberg Survey of about 2,500 filling stations in the Lower 48 states. But that figure "masks a tremendous variation" across the country, survey publisher Trilby Lundberg said.
"In most cities around the country, pump prices dropped as lower crude oil prices made their way all the way to the pump," Lundberg said. But at the same time, refining issues in California affecting gasoline supply caused huge price hikes there.
A power outage at one California refinery and a fire at another cut into supplies for much of the state and some neighboring markets, driving pump prices up by nearly 39 cents per gallon during the past two weeks, Lundberg said.
California Gov. Jerry Brown on Sunday ordered emergency steps to increase the state's gas supply and bring down prices.
Brown directed the state Air Resources Board to do whatever necessary to make an early transition to winter-blend gasoline, a mixture that evaporates more quickly than gas sold in summer. The move could increase the state fuel supply by as much as 10%, Brown's office said.
Nationwide, Lundberg said, gas prices should should start coming down soon.
"Looking around the corner, we see wholesale prices declining, and this should spell the end of the price hikes at the pump in the near future," she said.
Gas prices are up about 42 cents per gallon since early October 2011, she said.
The city with the cheapest average gasoline was Jackson, Mississippi, at $3.43 a gallon, according to the new survey. The most expensive could be found in San Diego, at $4.55.
Here are average prices in some other cities:
Baton Rouge, Louisiana: $3.50
Long Island, New York: $4.12
Portland, Oregon: $4.00
St. Louis: $3.46