Motorists may want to fill their gas tanks ASAP.

GasBuddy predicts prices in the region could rise 15 to 30 cents a gallon in the next week. At some Orange County stations, prices already have jumped 10 cents in a day.

The West Coast’s inventory of gasoline has declined by more than 1 million barrels while fuel imports to the area have been nonexistent, according to a report Wednesday by the U.S. Energy Information Administration.

Immediately following the report, wholesale prices spiked 27 cents a gallon.

Jerry Wynne, a Tustin resident, has seen prices rise already in his neighborhood.

“Last night, at the gas station, it was one price and early this morning it was a full 10 cents a gallon higher at all the stations, not just one,” he said Thursday.

Wynne said he drives a lot for work and that the price increase will “cost me a lot of money.”

The cost of gas per gallon has been falling since May, when prices peaked at $4. Allison Mac, a petroleum analyst at GasBuddy, suggested lower prices have kept overseas shipments from California because there is less profit to be made here.

There have been no major refinery issues reported recently. A Phillips 66 refinery in Wilmington is undergoing planned maintenance, which had a minor impact on supply, but it is not the only reason prices rose.

Jamie Court, president of the nonprofit Consumer Watchdog, said the rapid price increase is in large part a result of a manipulation of prices by the oil industry.

“There’s an opportunity to charge a premium in the market because of the tight supplies. There’s no good reason for the wholesale price of gasoline to go up this much,” Court said. “The problem is the oil refineries are keeping us running on empty to charge higher prices and make a larger profit.”

California has one of the highest gas prices in the nation because of high taxes and environmental standards. Court said California drivers pay an average of 74 cents more per gallon than the national average.

GasBuddy’s analyst doesn’t think the price hike will last long.

“Oil prices are still low,” Mac said. “It’s not going to be a continual increase.”

Marie Montgomery, a spokeswoman at the Automobile Club of Southern California, said she didn’t have an explanation yet for the rapid price jump.

“We’ve seen many times before where the wholesale prices spike crazily and then very quickly go back down, so the hope is that this is what will happen here too,” she said.

“A panic is going on, then when the buyers (gas station owners) receive more balanced information, the prices go back down very quickly. It’s good for consumers that the retail prices don’t move as often as the wholesale ones do, which can spike and bottom out, one day to the next.”

At least one area Costco might have been impacted by the inventory crunch. The big-box retailer on Technology Drive in Irvine reportedly ran out of 87-octane gas Thursday and offered customers its premium gas at the lower octane price.

Mac said Tesoro refineries on Thursday shut down supplies to unbranded wholesalers in California in response to the tightening supply. Although supplies are tight, Tesoro will supply only major chains under contract, not independent outfits, she said.

Staff writer Bianca Almada contributed to this report.

Contact the writer: hmadans@ocregister.com Twitter: @HannahMadans