Yes, blending premium and regular gasoline usually creates a mid-grade mix, and most engines handle it fine unless premium is required.
If you’ve got half a tank of 87 and only 93 is available, or the other way around, you’re not about to ruin your car. Gasoline grades mix together in the tank, and the result lands somewhere between the two octane ratings. In plain terms, that means 93 and 87 usually blend into something close to 90 or 91, depending on how much of each you add.
That said, whether it makes sense is a different question. Some engines are built for regular and gain little from premium. Others are tuned for premium and may lose power or efficiency if the octane drops too low. So the real answer isn’t just “yes.” It’s “yes, with a few limits that matter.”
What Mixing 93 And 87 Gas Actually Does
The number on the pump is an octane rating. Octane does not tell you how “strong” the fuel is. It tells you how well the fuel resists knocking, which is uncontrolled combustion inside the engine. The U.S. Energy Information Administration explains that higher-octane gasoline is made for engines that run with more compression and need more knock resistance. EIA’s octane overview lays out that relationship clearly.
So when you mix 93 and 87, you are not creating a dangerous chemical soup. You are blending two compatible grades of gasoline that differ mainly in octane. Your car sees one combined fuel in the tank, not two separate layers.
If the tank already has 87 and you add 93, the octane rises. If the tank already has 93 and you add 87, the octane falls. That’s the whole game. The final number depends on the ratio, not on which one went in first.
Why Many Drivers End Up With Mid-Grade By Accident
This happens all the time. A driver grabs the wrong pump handle, switches grades because one pump is out, or tops off with whatever is available during a trip. Gas stations even sell mid-grade by blending regular and premium at the pump, so the idea itself is normal.
The Federal Trade Commission’s fuel rating rules also make clear that gasoline is sold and labeled by octane rating. That label is there so drivers can match the fuel to the vehicle’s needs, not because mixing grades is forbidden. FTC fuel rating guidance explains how those ratings are determined and posted.
When Mixing Makes Sense And When It Doesn’t
For a car that calls for 87, adding some 93 is usually just extra spend. You may not notice any gain at all. AAA notes that vehicles built for regular gasoline usually cannot make extra horsepower just because premium is in the tank. AAA’s premium fuel research says the safest move is to follow the owner’s manual.
For a car that says premium is “recommended,” mixing can be a workable short-term move. Many modern engines can adjust timing to deal with lower octane, though you may feel softer acceleration or see a small drop in fuel economy. For a car that says premium is “required,” mixing down too far is a poor bet. One fill-up probably won’t destroy the engine, but repeated use can lead to knock, reduced performance, and extra strain.
Turbocharged engines, performance engines, and some luxury models are the ones that deserve the most caution. They tend to be tuned around higher octane. If your fuel door or manual says “premium required,” take that wording seriously.
| Situation | What The Mixed Fuel Means | Smart Move |
|---|---|---|
| Car requires 87 | Mixing 93 with 87 raises octane above what the engine needs | Fine to do, though usually not worth the added cost |
| Car recommends 91 or 93 | A mix may land near mid-grade and still run acceptably | Okay once in a while; return to the recommended grade next fill-up |
| Car requires 91 or 93 | Adding enough 87 can pull the tank below the needed octane | Avoid unless you have no other option |
| Half tank of 87, topping with 93 | Final octane usually ends up near 90 | Useful if you want a temporary mid-grade blend |
| Half tank of 93, topping with 87 | Final octane usually ends up near 90 | Usually fine for engines that only recommend premium |
| Accidental wrong-grade fill | One-time mix is rarely a crisis | Drive gently and refill with the proper grade when you can |
| Knocking or pinging starts after fueling | Octane may be too low for the engine load | Ease off hard acceleration and refill with the proper grade soon |
| Road trip in an area with limited pump choices | Blending may be the only practical way to stay close to target octane | Use the highest grade available and avoid full-throttle driving |
Can You Mix 93 And 87 Gas In A Premium Car?
You can, but the answer depends on the wording in your manual. “Recommended” gives you more wiggle room than “required.” That single word changes the risk level.
If Premium Is Recommended
Most of the time, the car’s engine control system can adapt. You might lose a bit of punch when merging or climbing hills. The car may also pull back ignition timing to prevent knock. That means the engine still runs, just not at its sweet spot.
In this case, mixing 93 and 87 now and then is usually not a big deal. It’s more of a performance choice than a mechanical threat.
If Premium Is Required
This is where drivers should slow down and read the label closely. Engines that require premium often depend on higher octane to prevent knock under load. Running too much 87 can leave less margin during hot weather, towing, steep grades, or hard acceleration.
If you made a one-time mistake, don’t panic. Keep revs modest, skip aggressive driving, and refill with the proper grade soon. What hurts is making low-octane fuel a habit in an engine designed around premium.
How To Estimate The Blend In Your Tank
The math is simple enough to do in your head. Multiply each fuel grade by the gallons added, add those totals together, then divide by total gallons. That gives you a rough octane level for the tank.
- 5 gallons of 87 plus 5 gallons of 93 lands near 90
- 10 gallons of 87 plus 2 gallons of 93 lands near 88
- 3 gallons of 87 plus 9 gallons of 93 lands near 91.5
You don’t need perfect math for daily driving. The broad point is enough: a small splash of premium into a mostly regular tank won’t turn it into premium, and a small splash of regular into a mostly premium tank won’t destroy the octane either.
| Blend Example | Approximate Octane | Typical Use Case |
|---|---|---|
| 50% 87 + 50% 93 | 90 | Common “mid-grade” style mix |
| 75% 87 + 25% 93 | 88.5 | Mostly regular with a premium top-off |
| 25% 87 + 75% 93 | 91.5 | Mostly premium with a regular top-off |
| 90% 87 + 10% 93 | 87.6 | Regular tank with a small premium add |
What You’ll Notice After Mixing
In a regular-fuel car, maybe nothing at all. That’s common. Engines built for 87 usually don’t gain much from extra octane, so the car may feel exactly the same.
In a premium-tuned car, the clues are usually subtle. Throttle response can feel softer. Passing power may dip. Fuel economy may slide a bit if the engine pulls timing to protect itself. On the flip side, if you’re only mixing a little and staying close to the recommended grade, you may notice nothing obvious during ordinary driving.
Actual knocking, rattling, or pinging is the red flag. If that starts after you fueled up, the octane may be too low for the load and conditions. Back off hard driving and refill with the proper grade as soon as you can.
What To Do If You Mixed The Wrong Gas
If the mix was 93 and 87, there’s rarely a need to drain the tank. This is not like filling a gasoline car with diesel. The grades are compatible. The issue is octane, not contamination.
- Check your fuel door or owner’s manual for “recommended” versus “required.”
- If premium is only recommended, drive normally and refill with the preferred grade next time.
- If premium is required, drive gently until you can bring the octane back up.
- If the engine knocks, avoid hard acceleration and refill sooner rather than later.
For most drivers, that’s enough. No drama. No tow truck. Just a smart refill plan.
The Real Rule For Daily Fill-Ups
Mixing 93 and 87 gas is usually safe because the fuels are meant to be compatible and the octane simply averages out. The part that matters is your car’s design. If it runs on 87, premium is often wasted money. If it recommends premium, a mix can be a workable stopgap. If it requires premium, don’t make a habit of pulling the octane down.
So yes, you can mix them. Just let the manual set the boundary, not the pump menu.
References & Sources
- U.S. Energy Information Administration.“Gasoline Explained: Octane In Depth.”Explains what octane measures and why higher-octane fuel is used in engines that need more knock resistance.
- Federal Trade Commission.“Complying With The FTC Fuel Rating Rule.”Shows how gasoline octane ratings are determined, certified, and posted at retail pumps.
- AAA.“Premium Fuel Research.”States that vehicles designed for regular gasoline usually do not gain extra power or savings from premium fuel and should follow the manufacturer’s recommendation.
Certification: BSc in Mechanical Engineering
Education: Mechanical engineer
Lives In: 539 W Commerce St, Dallas, TX 75208, USA
Md Amir is an auto mechanic student and writer with over half a decade of experience in the automotive field. He has worked with top automotive brands such as Lexus, Quantum, and also owns two automotive blogs autocarneed.com and taxiwiz.com.