Follow this route and you are basically driving a piece of Route 66 history. The cost to drive from Chicago to St. Louis is refreshingly modest, since both Illinois and Missouri keep gas near the national average, and Missouri often runs cheaper.
The I-55 run is about 300 miles down the old Mother Road corridor. Here is the fuel math across vehicles, where to fill up, and how classic Route 66 detours change the number.
What it costs to drive from Chicago to St. Louis
Here is the same trip at three common fuel-economy levels, based on about 300 miles and roughly $3.55 a gallon. Find where your car lands, and remember round-trip simply doubles it.
| Your car’s MPG | One-way | Round-trip |
|---|---|---|
| 20 MPG | $53.25 | $106.50 |
| 30 MPG | $35.50 | $71.00 |
| 40 MPG | $26.63 | $53.25 |
Those figures assume a fairly efficient car. Drive something thirstier, or hit mountains, heat, or heavy traffic, and your real number climbs. That is exactly why it helps to price the trip by your own vehicle rather than a generic average. And remember, the gas figure is per car, not per person: split it among three or four passengers and the Chicago to St. Louis drive becomes one of the cheapest ways to travel, often beating a single plane ticket outright.
How your vehicle changes the cost to drive from Chicago to St. Louis
The number that matters most is not the pump price. It is your car. On a 300-mile drive at about $3.55 a gallon, the gap between a thrifty hybrid and a thirsty pickup is dramatic. Here is the same trip across five common vehicle types so you can see where yours lands.
| Vehicle type | One-way gas | Round-trip gas |
|---|---|---|
| Hybrid (~48 MPG) | $22.19 | $44.38 |
| Compact car (~38 MPG) | $28.03 | $56.05 |
| Midsize sedan (~30 MPG) | $35.50 | $71.00 |
| SUV / crossover (~24 MPG) | $44.38 | $88.75 |
| Pickup / large SUV (~17 MPG) | $62.65 | $125.29 |
See the spread? Swapping a 17-MPG truck for a 30-MPG sedan can cut the fuel bill for this route roughly in half. If you own more than one vehicle, this table alone can tell you which one to take, which is a small decision that quietly saves real money over a year of trips. Real-world mileage tends to run 10 to 15% below the window sticker, thanks to how you drive, tire pressure, cargo weight, and even the weather, so measure yours with the MPG calculator before you trust any estimate. Then run your own figure through the gas cost calculator for a number matched to your exact car, and use the fuel consumption calculator to see the gallons you will actually burn.
The real cost is more than gas
Fuel is the headline, but it is rarely the whole bill. The main I-55 route is toll-free, so gas is essentially your only road cost. Then there is the stuff most people forget: coffee and snacks at every stop, a meal or two on a longer haul, and the slow, invisible cost of wear on your tires, brakes, and engine.
That wear is real money. When you price a trip by cost per mile instead of gas alone, you capture maintenance and depreciation too, which is how rideshare and delivery drivers think about every mile. A good habit is to pad your fuel estimate by 10 to 15% to cover the odd detour, an unexpected price jump, or a heavier load than planned, so you are never caught short at the pump. For a clean way to line up fuel, tolls, food, and lodging for this trip, drop them into the gas budget worksheet and you will get a number you can actually plan around.
What moves the price on the Chicago to St. Louis drive
Illinois versus Missouri pricing. You start in Illinois, where taxes can lift prices, and finish in Missouri, one of the cheaper states in the country. Waiting to fill up in Missouri can save you real money on the return leg.
Flat, straight highway. I-55 is easy on fuel, so a steady cruise keeps your MPG high across the whole trip.
Route 66 detours. If you follow the historic alignment for fun, expect extra miles and slower going, which adds a little fuel. Budget for it if that is part of the plan.
Where to fill up cheapest on the Chicago to St. Louis drive
Missouri typically undercuts Illinois, so fill up in Missouri, especially for the return trip toward Chicago. Around Chicago, higher Illinois taxes make city stations pricey, so top off in the southern Illinois stretch or wait for the Missouri side. Skip the interstate-exit stations right off the ramp and use a price app to find a cheaper pump a short distance away.
Before you leave, glance at the live gas price tracker so you know what a good price looks like, and compare state-by-state averages on the gas prices by state page. On the road, a gas price app will point you to the cheapest pump near your exit instead of the first flashy sign off the ramp, which is often the priciest.
Should you drive, fly, or take the bus?
There is a short flight, but for a roughly four-and-a-half-hour drive it rarely pays once you count airport time on both ends. Driving is cheaper, especially with passengers, and lets you sample the Route 66 landmarks that make this corridor famous.
The rule of thumb: driving usually wins when you are splitting fuel between passengers or need your car at the destination, while flying or the bus can win for a solo traveler on a longer route. Run the trade-off with the logic in our fly vs drive cost calculator guide before you book anything.
Doing this trip in an electric car?
If you are behind the wheel of an EV, the math flips in your favor. Covering 300 miles takes roughly 90 kWh for a typical electric car. Charge at home at normal residential rates and that works out to about $12.60 to $16.20 one-way, well under the $35.50 a 30-MPG gas car would burn. Lean on public DC fast chargers and it climbs to around $40.50, since fast charging costs more per kWh. Fast-charging along I-55 is decent and improving, so an EV handles this route with modest planning.
Charging prices swing a lot by state and network, so check EV charging prices by state and put the full comparison side by side with EV vs gas by state before you assume the plug always wins.
The best time to make the Chicago to St. Louis drive
Summer is peak Route 66 tourism season, with warmer driving and busier landmarks. A spring or fall weekday keeps traffic light and prices steady.
Prices also drift over the week. Gas is often cheapest early in the week and creeps up before the weekend, which we break down in our best day to buy gas guide. Time your fill-up accordingly and you shave a little off every gallon.
How to spend less on the Chicago to St. Louis drive
- Fill up in Missouri where prices dip. Confirm on the live tracker.
- Adding classic Route 66 stops? Recalculate miles in the road trip cost calculator.
- Compare state prices on the gas prices by state page.
- See where these states rank on the cheapest states for gas page.
- Driving an EV? Compare charging with the EV vs gas tool.
How we calculate the cost to drive this route
No black box here. The formula is simple: trip cost = (distance ÷ your MPG) × price per gallon. For the Chicago to St. Louis run we use a driving distance of about 300 miles and a blended pump price of roughly $3.55 a gallon across the states you cross. Swap in your own numbers for an exact figure. Our gas cost calculator does the arithmetic instantly, and the road trip cost calculator handles multi-stop trips.
Where the numbers come from: pump prices trace to the U.S. Energy Information Administration (EIA) weekly retail survey, refreshed on our state price pages every business day. Distances reflect the main highway route between the two cities. You can read exactly how each figure is sourced on our methodology and sources pages, and track longer trends on the gas price history page.
Calculations reviewed by Alex Morgan · Last reviewed: July 12, 2026
Frequently Asked Questions
How much does gas cost from Chicago to St. Louis?
About $36 one-way for a 30-MPG car at $3.55 a gallon, or roughly $71 round-trip. Missouri gas is often cheaper for the return.
How long is the drive from Chicago to St. Louis?
Roughly 300 miles on I-55, about four and a half hours without heavy traffic.
Does this route follow Route 66?
Yes, I-55 roughly parallels the historic Route 66 alignment, and you can detour onto original segments for the classic experience.
Is it cheaper to fly or drive?
Driving is usually cheaper once you count airport time, and it lets you enjoy the Route 66 landmarks along the way.
What would an EV cost on this route?
Charging at home and along the way, roughly $13 to $17 for the electrons, versus about $36 in gas.
The bottom line
Driving from Chicago to St. Louis costs most people between $26.63 and $53.25 in gas one-way, depending on the vehicle and the price on the day, with round-trip simply double that. The two levers you actually control are which car you take and where you fill up. Nail both, and you keep real money in your pocket.
Before you go, run your exact numbers in the gas cost calculator and check today’s live prices. Planning the whole route with stops? The road trip cost calculator maps every fill-up before you turn the key.