Patriots Day is the new Memorial Day, at least where gas prices are concerned.

The price of a gallon in Massachusetts shot up 18 cents over the last month, hitting $2.69 last week, eight cents higher than this time last year. Gas in Manchester, N.H., costs $2.64 a gallon, 18 cents higher than last month and six cents higher than last year.

There is a silver lining though, experts say. Prices should stabilize by next month and likely won't hit the $3 mark, Bob Cuomo, dean of the Girard School of Business at Merrimack College, said.

"I think you're going to find that prices are going to trend up a little bit longer," Cuomo said. But short of any nerve-inducing events in the Middle East, $3 won't happen, he said.

Merlin Hunt, a manager at Tally's on Washington Street, where regular unleaded was $2.83 yesterday, said that prices have been going up for the last month, and he blames the increase on offline gasoline refineries and, in particular, a major fire-damaged facility in Texas.

"There are a whole bunch of refineries that have problems, so they're not making enough to have gasoline in reserve. That's what's been making the price go up, supposedly," Hunt said.

The Energy Information Administration, a federal agency, says the national average of regular gasoline will peak at $2.87 in May. That's still 11 cents cheaper than gas was last July. Overall the price is expected to average $2.81 this summer.

A month ago, a gallon of gas in Massachusetts averaged $2.51, according to information from AAA.

"We historically see it going up around (Memorial Day)," Eleanor Baker, spokeswoman for AAA of Merrimack Valley, said. "It's all demand driven and that sort of thing, but this is a little early."

Cuomo attributed the early rise to a number of factors. Some are no surprise, he said. Demand is choked slightly each spring as refineries make the switch from producing heating oil to producing gasoline.

But new to the price-guessing game is the impact of regulations requiring a minimum portion of gasoline to be renewable fuel. That means oil companies are producing more grades of gasoline than in the past. And with the economy growing in China and India, there is more demand worldwide, Cuomo said.

On top of all of that is the wildest variable of all - what's going on in Iraq, Iran and the rest of the Middle East.

As the Iraq war stretches into its fifth year, bad news can jolt gas prices up. Cuomo attributed much of the recent jump to Iran's decision to capture and detain British sailors. Iran claims the sailors entered Iranian waters, a fact Britain disputes.

"The fear was that would lead to an expansion of conflict in the Middle East, choking off supply in Iran," Cuomo said.

Fuel Fears

Average gas prices nationwide (as of April 12) per gallon

Boston $2.70

San Francisco $3.39

New York City $2.97

Atlanta $2.68

Denver $2.73

Dallas $2.73

Source: AAA