Montana vs South Dakota gas prices
Regular gas is $0.29 a gallon cheaper in South Dakota — $4.28 on a 15-gallon fill-up. The two share a border, so that gap is worth knowing before you cross it.
Montana
South Dakota| Grade | MT | SD | Diff. | |
|---|---|---|---|---|
| Regular | $4.28 | $4.00 | $0.29SD | South Dakota |
| Midgrade | $4.61 | $4.19 | $0.42SD | South Dakota |
| Premium | $4.97 | $4.71 | $0.26SD | South Dakota |
| Diesel | $5.09 | $4.90 | $0.19SD | South Dakota |
Where the $0.29 gap actually comes from
11% of it is tax. Montana charges $0.03 more per gallon in federal and state taxes than South Dakota. The remaining $0.25 is a real difference in what the fuel, refining and distribution cost — refinery proximity, pipeline access and state fuel-blend rules.
Fuel, refining, distribution and marginFederal and state taxes Pre-tax figures are estimates — see the note below.
What the gap is worth
Based on today’s $0.29 per-gallon difference, which moves week to week. Use the fuel cost calculator for your own mileage and vehicle.
Prices by metro area
State averages hide a lot. These are the cheapest metros AAA reports on each side.
Other comparisons
Frequently asked questions
Is gas cheaper in Montana or South Dakota?
Regular gas is cheaper in South Dakota, at $4.00 a gallon against $4.28 in Montana — a gap of $0.29, or 7.1%. On a 15-gallon fill-up that is $4.28. Figures are AAA daily state averages for 2026-08-02.
Why is gas more expensive in Montana?
11% of the $0.29 gap is tax rather than the cost of the fuel. Montana levies $0.03 more per gallon in federal and state taxes; the remaining $0.25 is a genuine difference in what the fuel, refining and distribution cost.
Is diesel cheaper in Montana or South Dakota?
Diesel is cheaper in South Dakota at $4.90 a gallon, against $5.09 in Montana — $0.19 a gallon apart.
Is it worth crossing from Montana into South Dakota to fill up?
If you are already near the line, yes: a 15-gallon fill saves about $4.28. Driving out of your way for it rarely pays — at $4.28 a gallon and 25 mpg, a 12-mile round trip would eat the whole saving in fuel alone, before your time.