Illinois vs Wisconsin gas prices
Regular gas is $0.52 a gallon cheaper in Wisconsin — $7.77 on a 15-gallon fill-up. The two share a border, so that gap is worth knowing before you cross it.
Illinois
Wisconsin| Grade | IL | WI | Diff. | |
|---|---|---|---|---|
| Regular | $4.63 | $4.11 | $0.52WI | Wisconsin |
| Midgrade | $5.20 | $4.65 | $0.55WI | Wisconsin |
| Premium | $5.73 | $5.25 | $0.48WI | Wisconsin |
| Diesel | $6.26 | $6.13 | $0.13WI | Wisconsin |
Is cheaper gas worth the detour?
Use your tank and extra travel costs. Prices below are AAA state averages as of 2026-09-16; check the actual station prices before driving.
Extra distance and time include the return to your original route. Detour fuel uses the higher state price. Tire wear and maintenance are excluded. This estimates a price difference; it does not verify a station offer or route.
Where the $0.52 gap actually comes from
66% of it is tax. Illinois charges $0.34 more per gallon in federal and state taxes than Wisconsin. The remaining $0.18 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 Local county and city fuel taxes are not included, and Illinois permit them. Pre-tax figures are estimates — see the note below.
What the gap is worth
Based on today’s $0.52 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 Illinois or Wisconsin?
Regular gas is cheaper in Wisconsin, at $4.11 a gallon against $4.63 in Illinois — a gap of $0.52, or 11.2%. On a 15-gallon fill-up that is $7.77. Figures are AAA daily state averages for 2026-09-16.
Why is gas more expensive in Illinois?
66% of the $0.52 gap is tax rather than the cost of the fuel. Illinois levies $0.34 more per gallon in federal and state taxes; the remaining $0.18 is a genuine difference in what the fuel, refining and distribution cost.
Is diesel cheaper in Illinois or Wisconsin?
Diesel is cheaper in Wisconsin at $6.13 a gallon, against $6.26 in Illinois — $0.13 a gallon apart.
Is it worth crossing from Illinois into Wisconsin to fill up?
If you are already near the line, yes: a 15-gallon fill saves about $7.77. Driving out of your way for it rarely pays — at $4.63 a gallon and 25 mpg, a 21-mile round trip would eat the whole saving in fuel alone, before your time.
Why this price is what it is
- Premium vs. Regular Gas: Is Premium Actually Worth It?Premium costs more per gallon — but does it help your car? Here's when premium is worth it, when it's wasted money, and what octane really does.
- Fuel Taxes Explained: What You Really Pay Per GallonA big slice of every gallon is tax — but how much, and where does it go? A clear guide to federal, state and European fuel taxes.
- The Best Day and Time to Buy Gas (Backed by Price Data)Studies of billions of transactions point to early in the week as the cheapest time to fill up. Here's the best day, the best time of day, and why it works.