Is Premium Gasoline Actually Worth the Price At the Pump?

My Subaru WRX calls for 93-octane gasoline, but as a writer, my wallet doesn’t always agree. So once, I decided to fill it up with 87-octane instead. The result: I could actually hear the poor engine knocking for a week until I was able to fill up again. Wow, was there a big difference between regular and premium gas?

Despite the cost, I have never tried to undercut the octane again. But not all cars require that extra expense. Here’s what to know about regular vs. premium gas and how to figure out which is best for your car.

Regular vs. Premium Gas: What’s the Difference?

One obvious difference between regular and premium gasoline is the price. Premium gasoline, which is rated at 91 or 93 octane, can be 50 cents more expensive than regular octanes like 87 and 89. That’s because gas with higher octanes can withstand higher compression before detonating, meaning the higher the octane, the lower the likelihood the fuel will detonate at the wrong time. If detonation happens at the wrong time frequently, it can harm your engine.

“Most cars on the road are built to run efficiently on regular gas, which has an octane rating of 87,” says Xavier Sebastian, an automotive expert at Way.com. “Premium gas, with an octane rating at 91 or above, is better suited for vehicles with engines designed for higher performance.”

How Do I Know If My Car Needs Premium Gas?

The answer is usually in the owner’s manual or posted inside the fuel door. Cars that have high compression ratios or turbochargers usually need premium gas.

“If it says ‘premium fuel required,’ then you don’t have much choice,” says Sebastian. “Your engine is designed to run on high-octane fuel, and using regular gas could cause knocking or long-term damage.”

If your car’s manual says “premium recommended” or “regular fuel acceptable,” that means you don’t have to use premium gas. However, occasionally, a car will do better on a higher octane. For example, if you have an older car that’s designed for 87-octane gas and it knocks when you punch the pedal, try filling it with 89-octane fuel to see if the knock goes away. If so, keep using 89-octane to regain some power and save your engine.

“Fuel octane is also good information to factor into purchasing a car,” says Chris “Moose” Pyle, an automotive expert with JustAnswer. “Paying 20 to 50 cents more per gallon because the car needs high-octane fuel is not that enjoyable.”

Can I Use Premium Even If My Car Doesn’t Need It?

Yes, you can use premium gas even if your car doesn’t call for it, but don’t expect major benefits for the price difference. “Sometimes, higher octane fuels do contain a few more additives like fuel system cleaner and water reducer,” says Pyle. If your car runs much better on high octane but does not require it, this means your car has concerns that need to be diagnosed and resolved so you can stop spending so much at the pump.”

What Will Happen If I Use Regular Gas In My Car That Needs Premium?

You’ll likely notice a drop in power and fuel efficiency because the gas will prematurely ignite in the engine. Over time, this will also lead to carbon buildup, possible engine damage, spark plug problems and catalytic converter failure.

“The engine’s knock sensor will adjust to prevent serious damage, but over time, this constant adjustment can lead to extra wear and tear,” says Sebastian. “While your car will still run, it won’t perform at its best.”

Can You Mix Premium and Regular Gasoline?

Yes, but if you have a car that requires premium and you put in regular, your car might not run at its peak performance.

“It’s not a major issue if it happens occasionally, but for the best results, check your owner’s manual and stick to the recommended fuel to keep your engine running smoothly,” says Sebastian.

What To Do If I Drove With the Wrong Gas In My Car?

If you put too high an octane in, don’t worry; nothing will change. If you put too low an octane in, just drive normally, but take it a little easier with acceleration, especially if it feels like the car is lugging on uphill climbs. Once the tank gets low, refill it with the correct fuel.

“If the car is running badly, you can top off the tank daily with the correct fuel grade to slowly dilute the fuel and increase the overall octane,” says Pyle.

If you accidentally put diesel in instead of unleaded, do not start your car, but instead have it towed to a mechanic who can drain the tank before it does any damage.

Are There Any Gas Additives Worth Using?

No ‘magic’ or ‘revolutionary’ additives will increase your fuel efficiency. However, some owners like to add fuel-system cleaning additives periodically. Many companies make the type you add to your tank. The most effective ones have polyisobutylamine (PIBA) and polyetheramine (PEA), so look for one of those ingredients on the label. Follow the product’s directions for treat rates. Avoid all other gas additives!

About the Experts

• Chris “Moose” Pyle is a master-certified technician with 20-plus years of automotive experience. He has also worked as an expert for JustAnswer since 2006.
• Xavier Sabastian is an author and auto/insurance expert with the Way.com auto app.