For much of the last month, Mainers have enjoyed a rare treat: gasoline that’s gotten cheaper even while prices have soared nationally.

Now that trend is changing.

In general across the U.S., gas prices have been rising this fall, retracing many of the increases that hit in the spring, peaked in early June and subsided in late summer.

But in Maine, where gas climbed to over $5 a gallon in mid-June, prices continued to retreat through September and early October. They reached an average low of $3.48 a gallon last week, according to GasBuddy.com, which tracks fuel prices nationally.

At the same time that prices in Maine were bottoming out, the national average was $3.83 a gallon and rising. It plateaued slightly this week at just under $3.95 a gallon, according to the site.

Maine prices also have begun inching back up, although at $3.64 they remain almost 30 cents a gallon below the national average. Across the state, per-gallon prices on Tuesday day ranged from $3.36 a $3.99, with most of the higher prices in southern Maine, according to GasBuddy.

The website said refinery problems were behind rising prices in the Great Lakes region and West Coast, and said prices were lowest in Georgia (average $3.21) and in Mississippi and Texas ($3.25). Average prices were highest in California ($6.31 a gallon), Alaska ($5.53) and Oregon ($5.50).

There are a lot of reasons for the disparities in price, but the bottom line is supply and demand, said Charles Summers Jr., president of the Maine Energy Marketers Association.

Last week’s decision by OPEC+ to cut oil production is a big factor, he noted. But there are others, including the ongoing war in Ukraine and sanctions against Russia over the invasion of its neighbor – all introduce new questions into how much fuel the U.S. will have.

Summers said the Northeast has been affected by refinery shutdowns in Pennsylvania, so steps to increase supply, such as releasing oil from the national reserves in Texas and Louisiana, don’t have as much of an impact in this region as they might elsewhere.

But demand also has started to ease in the Northeast, where many employees continue to work from home and the peak driving season has passed.

In addition, a lot of the Northeast’s oil and fuel continues to come from Canada, and those supplies have remained stable this fall, as has its refining capacity. So the impact of the refinery shutdowns on supplies in New England is limited, at least in the short-term, Summers said.

All those factors create a “see-saw effect” on prices, he said, and only time will tell how they balance out later this fall and winter.

He declined to predict what might happen to costs in Maine, saying there are too many variables in play.

In the face of that uncertainty, the safest thing for oil companies and gasoline dealers is to put a “floor” under prices.

“The market does not like it when things are not clear and that tends to drive up the price,” Summers said.