Average gas prices in Maine hit $3.83 a gallon Tuesday, up 4 cents from the previous day and nearly a dollar in the past month, according to AAA.

When it comes to fuel costs, however, not every Maine county is equal. Throughout the surge in gas prices since the U.S. and Israel began the war against Iran, disrupting the production and shipping of oil in the Middle East, western Maine has been consistently among the most expensive in the state.

Though prices fluctuate, and drivers can always find deals station to station, you can generally expect to pay 5-8 cents a gallon more in Franklin, Oxford, Androscoggin and Kennebec counties. Washington County is frequently among those paying slightly higher prices at the pump as well.

On Tuesday, the highest average prices in the state were in Washington County ($3.88 a gallon), and Oxford and Lincoln counties (both $3.87), with Kennebec County right behind ($3.86).

Jonathan Rubin, professor of economics at the University of Maine, explains there are two primary reasons for the price difference.

“Refined products, gasoline, diesel, and so forth, they’re all either imported by pipeline or water to a small number of coastal terminals,” he said. The farther away from the coast or pipeline, the farther the product has to be moved, increasing the cost.

The other reason some areas see higher gas prices comes down to competition and volume.

“In smaller towns, although not exclusively, there’s less retail competition at the pump,” Rubin said Monday. “If you’re selling lower volumes of gasoline … you have to spread your capital costs. You’re holding this inventory for longer, and it’s expensive, so they have legitimate reasons that their costs for the small stations are just more expensive.”

Dan Goodman, the public affairs and traffic safety manager at AAA of Northern New England, offered essentially the same explanation for the higher prices.

“It is a rural area with fewer gas stations, which reduces competition,” he said. “Stations there also sell less fuel, so they have to charge more per gallon to cover their costs. In addition, fuel has to be transported farther from refineries in places like New Jersey, often by truck, which increases delivery costs.”

Maine, like 20 other states, has no oil refinery. However, Irving Oil operates Canada’s largest refinery in Saint John, New Brunswick.

Counties bordering Canada tend to have gasoline prices at the lower range of the average price. While he couldn’t say for sure without seeing the contracts, Rubin said he suspects the proximity to the St. John refineries is a factor.

Nationally, AAA reported gas prices hit an average of $3.97 a gallon Tuesday.