Average gasoline prices in Montana have fallen 6.4 cents per gallon in the last week, averaging $3.13/gallon on Monday, Dec. 4, according to GasBuddy’s survey of 615 stations in Montana. Prices in Montana are 44.7 cents per gallon lower than a month ago and stand 27.6 cents per gallon lower than a year ago. The national average price of diesel has fallen 4.7 cents in the last week and stands at $4.18