Illinois vs Missouri gas prices
Regular gas is $0.56 a gallon cheaper in Missouri — $8.37 on a 15-gallon fill-up. The two share a border, so that gap is worth knowing before you cross it.
Illinois
Missouri| Grade | IL | MO | Diff. | |
|---|---|---|---|---|
| Regular | $4.35 | $3.79 | $0.56MO | Missouri |
| Midgrade | $4.94 | $4.16 | $0.77MO | Missouri |
| Premium | $5.46 | $4.51 | $0.95MO | Missouri |
| Diesel | $5.32 | $4.87 | $0.46MO | Missouri |
Where the $0.56 gap actually comes from
66% of it is tax. Illinois charges $0.37 more per gallon in federal and state taxes than Missouri. The remaining $0.19 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 $0.56 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 Missouri?
Regular gas is cheaper in Missouri, at $3.79 a gallon against $4.35 in Illinois — a gap of $0.56, or 14.7%. On a 15-gallon fill-up that is $8.37. Figures are AAA daily state averages for 2026-08-02.
Why is gas more expensive in Illinois?
66% of the $0.56 gap is tax rather than the cost of the fuel. Illinois levies $0.37 more per gallon in federal and state taxes; the remaining $0.19 is a genuine difference in what the fuel, refining and distribution cost.
Is diesel cheaper in Illinois or Missouri?
Diesel is cheaper in Missouri at $4.87 a gallon, against $5.32 in Illinois — $0.46 a gallon apart.
Is it worth crossing from Illinois into Missouri to fill up?
If you are already near the line, yes: a 15-gallon fill saves about $8.37. Driving out of your way for it rarely pays — at $4.35 a gallon and 25 mpg, a 24-mile round trip would eat the whole saving in fuel alone, before your time.