Gasoline prices on O'ahu could rise as much as 18 cents per gallon next week as the state's new gas cap law links Hawai'i prices to rapidly climbing prices on the Mainland.

Hurricane Katrina caused a spike in Mainland gasoline prices yesterday that will be factored into Hawai'i prices.

Wholesale gasoline prices in Gulf Coast markets soared by 54 cents a gallon following reports that more than 8 percent of U.S. refining capacity had been shut down as a precaution ahead of the storm.

The price of crude oil futures jumped to more than $70 a barrel in New York before giving up most of the gain after the storm spared New Orleans from a direct hit.

One analyst said pump prices nationwide likely would average more than $2.75 a gallon by week's end — up from $2.61 a gallon last week, according to Energy Department data.

All this comes as Hawai'i is set to become the only state in the nation with government-imposed gasoline prices.

On Thursday the state's gas cap goes into effect.

For the first four days, it will set Honolulu's wholesale regular gasoline price cap at $2.76, including taxes. But that is just the cap on wholesale prices.

What you pay at the pump will depend on whether wholesalers price at the maximum and retailers add their usual 12-cent markup. If they do, you'll be looking at pump prices of around $2.88 on Thursday.

That's a few cents higher than the average retail price for regular in Honolulu yesterday of $2.82 a gallon, according to yesterday's AAA Daily Fuel Gauge Report.

The effect of Katrina on Hawai'i gas prices will first be felt starting Sept. 5 when the price cap is updated to reflect changes of the past week.

If the current price trend on the Mainland continues, the wholesale price cap for regular on O'ahu will be raised 18 cents on Sept. 5 to $2.94. That could mean pump prices of $3.06.

Right now refiners aren't predicting what will happen once the price caps take effect.

"We just don't know what to expect," said Albert Chee, a spokesman for Chevron Corp., which owns one of the state's two refineries. "We just have to wait and see how the market rationalizes around a new factor, which is the price cap."

Supporters of the price cap say the increase in Hawai'i prices will not be because of the gas-price cap, but because of events that raised prices on the Mainland.

"Even without the cap, I think that price increases are very possible," said Sen. Ron Menor, D-17th (Mililani, Waipi'o), an architect of the price-cap law. "To that extent, I don't think the price cap should be blamed for those increases."

Reach Sean Hao at shao@honoluluadvertiser.com.