Illinois vs Kentucky gas prices
Regular gas is $0.65 a gallon cheaper in Kentucky — $9.75 on a 15-gallon fill-up. The two share a border, so that gap is worth knowing before you cross it.
Illinois
Kentucky| Grade | IL | KY | Diff. | |
|---|---|---|---|---|
| Regular | $4.35 | $3.70 | $0.65KY | Kentucky |
| Midgrade | $4.94 | $4.24 | $0.70KY | Kentucky |
| Premium | $5.46 | $4.68 | $0.78KY | Kentucky |
| Diesel | $5.32 | $4.96 | $0.37KY | Kentucky |
Where the $0.65 gap actually comes from
58% of it is tax. Illinois charges $0.38 more per gallon in federal and state taxes than Kentucky. The remaining $0.27 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 $0.65 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 Kentucky?
Regular gas is cheaper in Kentucky, at $3.70 a gallon against $4.35 in Illinois — a gap of $0.65, or 17.6%. On a 15-gallon fill-up that is $9.75. Figures are AAA daily state averages for 2026-08-02.
Why is gas more expensive in Illinois?
58% of the $0.65 gap is tax rather than the cost of the fuel. Illinois levies $0.38 more per gallon in federal and state taxes; the remaining $0.27 is a genuine difference in what the fuel, refining and distribution cost.
Is diesel cheaper in Illinois or Kentucky?
Diesel is cheaper in Kentucky at $4.96 a gallon, against $5.32 in Illinois — $0.37 a gallon apart.
Is it worth crossing from Illinois into Kentucky to fill up?
If you are already near the line, yes: a 15-gallon fill saves about $9.75. Driving out of your way for it rarely pays — at $4.35 a gallon and 25 mpg, a 28-mile round trip would eat the whole saving in fuel alone, before your time.