Nationwide gasoline prices have been climbing for 20 straight days now, and although Montana enjoys the cheapest prices in the country, it is one of the few states experiencing higher prices than last year.

"[In Montana,] right along with what we expected, prices jumped another 6 cents per gallon. Currently averaging about 3.13, still about a dime cheaper than last year, but prices are moving up," said gasbuddy.com Petroleum Analyst Patrick Dehaan. "They likely will do so this week. In fact, in Montana there is only one pump in the state under $3.00, that's the Sam's Club in Great Falls."

The price spike is due to low supply because of refinery maintenance.

"There's a lot of maintenance talking place in the Rockies that's resulting in a drop of supply," Dehaan said. "Prices are edging higher, in fact, prices could really take off this week, with an average increase of another four to eight cents per gallon. So be ready, higher prices will be coming."

DeHaan says the rising prices are likely to continue at least until May, and possibly even longer.