Ever stare at the row of numbers at the gas station and wonder what this all means? Why do some gas stations go all the way up 93 while others stop at 91?

The difference between 91 vs 93 octane is simply that the higher number has a higher resistance to detonation. That’s the difference between all octane ratings at the pump actually; 87, 89, 91, 93, 95, and so on.

Whether or not that is useful depends on your vehicle’s engine and its requirements for fuel. A quick way to tell is to look inside your fuel filler door. It will say which fuel is needed for your car.

If it says premium fuel “required” then only the best will do. If it only says a certain octane is “recommended” then you can use a lower octane without hurting your engine but, will likely not get the most performance from your car.

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Table of Contents

• Why Is Octane Important?
• Can I Use 91 And 93 Octane Interchangeably?
• What Are The Effects Of Using The Wrong Octane Fuel?
• Is Midgrade Fuel A Ripoff?
• Can I Use Octane Booster In Place Of Premium Fuel?
• Will Higher Octane Offer Better Fuel Economy?
• What Is The Best Octane For My Car?
• In Sum

Why Is Octane Important?

According to the Fuel Freedom Foundation “octane is the measure of how much compression a fuel can withstand before igniting.” The higher the fuel’s octane rating, the more resistance it has to premature detonation in your engine. So what does this mean practically?

87 octane which we commonly refer to as regular ignites more easily in your engine. You would think this is a good thing right? For most cars, it doesn’t matter but for high-performance engines with tight tolerances, it matters a lot.

See in the combustion process the fuel, air, and spark all come together to ignite and create the explosion (also known as combustion) that runs the engine. This is the primary motive force of your car.

Using the right octane fuel for your car is required to make sure all the components of the engine work according to their intended design. That means when combustion occurs that all the components are where they should be in sequence.

Can I Use 91 And 93 Octane Interchangeably?

91 and 93 octanes are both considered premium fuel. In fact, you’ll only see one of the two at any given gas station and not both. That’s because 91 octane is available in higher altitude areas whereas 93 is not.

The lack of oxygen at higher altitudes makes 91 octane more resistant to detonation and therefore it works just like higher octane 93 at sea level. So you can in fact use them interchangeably without damaging your engine.

What Are The Effects Of Using The Wrong Octane Fuel?

The effects of wrong octane fuel may not be immediately apparent but can damage your vehicle in significant ways. Depending on which fuel you use, and what your vehicle is designed for it can be severe.

The key thing to remember is that you can always go higher in octane than your vehicle requires and not damage your vehicle but, never lower.

For example, if your car requires 87 you can put in 93 with no issues but, if it requires 93 you can not put anything lower.

Using lower octane fuel will result in poor fuel economy and reduced power with possible warning lights on the dash.

Premature detonation from low octane can also damage pistons and rings in the engine. Prolonged use of the wrong fuel will eventually totally destroy the engine.

Is Midgrade Fuel A Ripoff?

Midgrade fuel is generally 89 octane and you’ll see very few cars that require this fuel. Most vehicles run on either regular 87 or premium fuel only.

In my opinion midgrade is generally a marketing play by gas stations to trick customers into thinking they are getting better fuel for their car.

Midgrade is only slightly less expensive than premium fuel and only slightly higher octane than regular, so it’s the lowest return for your fuel investment.

If your car runs on 87 then there’s no need to go up unless you want a performance increase. If that’s the case premium is the better choice as you’ll get higher outputs vs the price you pay.

Can I Use Octane Booster In Place Of Premium Fuel?

Octane boosters are additives you can purchase from auto parts places that can raise the octane level of your fuel if you can not find premium fuel or higher at the gas station.

They do work and can save you from damaging your engine if you happen to find yourself in a place that doesn’t offer anything higher than regular octane gas.

It’s hard to tell exactly what the octane rating will be when mixed without testing the fuel so it’s best to keep this as a last resort and not a replacement for getting premium fuel.

Just a quick note. All fuels now contain ethanol to achieve higher octane ratings so chances are that the octane booster you will be using will contain that.

This doesn’t mean however that you can use e-85 or other ethanol blends directly from the pump. Your car has to be flex-fuel capable in order to use ethanol. For more information on e-85 check out our article that demystifies this alternative fuel.

Will Higher Octane Offer Better Fuel Economy?

This is a bit controversial as some vehicles respond differently than others. The general consensus is that using higher octane fuel than what your vehicle requires doesn’t provide any economic benefits.

However, anecdotally some cars respond better to higher octane fuels and may show a slight increase in the economy. This is not a guarantee and is something you would need to experiment with to see if it works.

In my experience cars just seem to run a little bit better on premium but it might just be a placebo.

The theory is that higher octane fuel is more refined and generally a cleaner burning fuel than regular which can have impurities. So if your vehicle runs a cleaner fuel with fewer impurities it might give a slight bump in the economy.

Again no hard science points to this, just a gear-heads intuition.

What Is The Best Octane For My Car?

The best octane for your vehicle is what the manufacturer recommends. Some vehicles have requirements for a lower octane but suggest higher ones for maximum performance.

Remember required and recommended are the key difference. Required is the minimum octane allowed for your car to function properly, while recommended is the octane rating suggested for maximum performance.

For example, my 2007 Toyota Camry has a 2grfe V6 engine that can run on 87 octane quite happily. However, I use premium 93 octane as I have found better performance and responsiveness from the engine, as well as a slight bump in fuel economy.

If you stick to what the manufacturer recommends you can be assured that the vehicle is running the way the engineers intended it to at its peak. However, if your vehicle runs well for you at its required octane then that’s fine too.

In Sum

91 and 93 octane are generally the same things just found in different places. What’s more important is using the best fuel your car can utilize.

Stick to the fuel you feel works the best in the engine of your car with respect to the octane requirements. Sometimes that may be higher than what the vehicle requires and for others it may be exactly the bare minimum.

Try to purchase fuel at the same locations as the consistency of fuel is also an important factor. If you know a gas station isn’t as busy as other places chances are that fuel will be older and has higher chances for impurities.

Also one last note; gas does go bad after a while and doesn’t last forever so use it or lose it. If your vehicle will be stored or sits around a lot use a fuel additive that prevents the fuel from deteriorating.