Average gasoline prices in Montana have fallen 1.8 cents per gallon in the last week, averaging $3.44/g Monday, May 20, according to Gas-Buddy's survey of 615 stations in Montana. Prices in Montana are 12.2 cents per gallon lower than a month ago and stand 9.4 cents per gallon lower than a year ago. The national average price of diesel has fallen 3.3 cents in the last week and stands at $3.86