Did you know that in 2020, even during the pandemic, Americans used ~123 Billion gallons of motor gas? That equates to 337 Million gallons per day! (U.S. Energy Information Administration) Unfortunately many of these drivers are not fully aware of all the gas they are putting into their vehicles. The most common question by drivers is “what is e85 gas?”. The next common question is “What is octane?”. This article sets out to explain that, and more.

In the modern day, car manufacturers have been increasingly requiring the use of higher octane in their engines, especially engines designed for performance. More and more, the cost difference between regular (87) and Premium (93) gas has been becoming greater. So more than ever, drivers should understand what they put into their vehicle, and whether the higher costs are worth it.

woman in yellow shirt while filling up her car with gasoline octane ethanol knocking
Photo by Andrea Piacquadio on Pexels.com

Octane explained

Octane numbers, such as 87, 91, 93, are simply measures of stability. Commonly referred to as the anti-knock number. The higher the number, the higher the stability.

Stability is the pressure at which the fuel will spontaneously combust (auto-ignite) with an engine (inside the cylinder combustion chamber).

The octane number is a result of a calculation of two rating, averaged amongst each other. The equation is: Research Octane Rating (RON) + Motor Octane Rating (MOR)/2. This gives the final octane rating you see on the pump itself. (R+M/2)

The higher the rating, the higher the anti-knock properties of the gas.

Octane levels do not equate to energy levels. They never have, and they likely never will.

Commonly available octane

trukbed mustang gas station octane gas pump ethanol

Common types of octane numbers seen at station pumps (depending on where you live and the brand of gas) are usually 87, 88, 89, 90, 91, 93, and 94.

87 is usually the ‘regular’ octane, 89-90 are often referred to as ‘mid-grade’, and 91 and over are considered the ‘premium’.

The names each brand or station may use to title these octane levels may differ from one to the other, so focus on the actual numbers.

What are “grades” of fuel?

When people refer to “grades” of gas or fuel, the term “grade” actually refers to the mix, or composition of the gas itself, not necessarily the octane. So, “grade” is not synonymous with “octane”.

You may have heard of the terms ‘winter-grade’ and ‘summer-grade’. Different locations and/or seasons play a factor as to which particular grade is available. Some regional laws dictate the actual fuel types, and grades that are allowed to be offered in the area based on legislative efforts to reduce air pollution and emissions.

These regulations result in different gas chemical compositions in different times of the year, in different locations.

Gas is never just gas, and is not the same from one brand to another, nor is it the same from one region to another. It further is not the same from one season to another.

The difference between Summer and Winter Grades

What makes a summer-grade differ from winter-grade? The actual vapor pressure. In colder weather , vapor needs to be higher to start an engine. In the warmer weather, vapor needs to be low in order to reduce harmful emissions.

So it may be easier to understand why a car that has winter-grade fuel in its system who tries to get through an emissions check of a warmer climate state might fail the test due to having too much vapor emission. Get the vehicle through a couple tanks of local fuel beforehand for a better chance at passing.

What’s ethanol? E85 explained

Ethanol is a renewable fuel made front plant materials. This is also known as and referred to as “biomass”. It is used in about 98% of all gas in the United States. Ethanol is clean and colorless.

The most common amount used in gas is 10% (E-10), where the 10 indicates the ethanol volume.

How and why is ethanol used in gas?

Gas uses ethanol because it oxygenates the fuel resulting in less air pollution.

Ethanol is mixed in with the gas we use for our cars and trucks at the fuel terminals. This is before the consumer sees it at gas stations, where it is shipped after mixing.

We end up with the mixtures that we see labeled at pumps, such as E10, E15, E85, etc. E85 is being seen more commonly, as that is the mixture certain engines designated as “Flex Fuel” are able, but not required, to use.

Further, E15 is 15% ethanol in volume, and is approved for use in any 2001 or newer light duty vehicle.

Is ethanol the same as octane?

While ethanol itself has a higher octane number than gasoline (see Octane section), it is not the same as gasoline. It is added to gasoline, and once mixed, will then help get certain gasolines to reach the desired octane level (87, 91, etc).

How does ethanol affect power and performance?

Despite having a higher octane number in an of itself, ethanol is less energy than gas. Therefore, Octane level, such as 91, 93 etc, does not equal energy level. Since ethanol is less energy than gas, the engine much work harder to achieve the engine operator’s desired power and performance. More consumption of ethanol must be had as a result.

Does ethanol in gas affect MPG (Miles Per Gallon)?

Fuel efficiency is impacted with the use of ethanol, and varies depending on the amount of ethanol blended into the gasoline. When large amounts of ethanol are used as a percentage to the gas (ratio), such as e85 (85% ethanol), or more, as much as 30% of energy can be lost. This will greatly reduce fuel efficiency in terms of consumption, but can be very beneficial to the environment.

Empty fuel warning light in car dashboard. 3D rendered illustration.

Fuel economy will be based on the amount of ethanol used in the mixture of gas, and whether or not the vehicle is specifically designed and engineered to effectively run on gas and/or ethanol. There is no hard and fast answer that pertains to all vehicles using gas mixed with ethanol.

It’s widely known in automotive circles that using lower than an engine manufacturer’s required octane levels will likely result in engine knocking. As discussed above, lower octane means a less stable fuel. The fuel and air will spontaneously combust too early, in an engine that wasn’t designed for it, and leave carbon build-up.

Persistent knocking will result in engine damage.

Using lower than required octane levels affects the air/fuel mixture (ratio) for which the engineers designed the engine. It is with this incorrect mix of air and fuel that knocking begins.

What is a “knocking” engine?

graphic displaying engine combustion knocking

Knocking can damage the the surface of the piston, cylinder walls and/or the crankshaft bearings.

Repairs can be costly, and even irreversible permanent damage can occur. This can result in a salvaged engine, or an extremely costly engine rebuild. As you can see, the cost savings one might believe they are getting by using the lesser priced fuel can easily, and quickly, end up costing more than was ever intended. It is simply just not cost effective.

Modern computer-controlled fuel injection technology helps to inhibit knocking when less than required octane is used. When done so, engine performance will surely suffer. This computer controlled technology does not fully prevent the damage that can occur.

What is “carbon build-up”?

Since lower octane ignites at a lower temperature and pressure, certain carbon deposits will remain. This creates an unwanted build-up of carbon deposits.

carbon build on on valves due to low octane

For most experienced engineers and automotive technicians, it is not difficult to determine when engine knocking has been the result of improper fueling. Since the science is well known and easy to prove, a manufacturer is likely to deny any warranty claim arising due to neglect.

What if NO other gas is available at the moment?

While damage to an engine due to knocking can occur quickly in an engine’s life, the damages are not instant. As mentioned, there are modern fuel injection systems to inhibit knocking. So, there is somewhat of a cushion, so to speak. Using lower than required fuel will be fine in a pinch scenario. There is no need to worry if one tank, or a few gallons, are used.

One idea to help combat this scenario is to keep accessible a bottle of octane booster from a reputable brand to help compensate for the lack of octane in the fuel being offered.

Unlike using LOWER than required octane, using higher than required or recommended will not hurt an engine. Higher octane does not equal higher energy. There is no specific energy gain out of an engine by using higher octane fuel.

Whether or not an engine will perform better with higher octane depends on the particular engine. Some engines are designed to handle it and achieve improved performance or MPG. Some simply were not. This means, while a manufacturer states 87 is the recommended fuel, it is hit or miss (likely, but not always) as to the positive results.

Millions of Americans spend hundreds of millions of dollars collectively each year buying premium octane gas when they didn’t need to.

high octane rating stic

The Car and Driver 4 vehicle test of 2019

Consider this test Car and Driver performed in 2019. They used higher and lower than required/recommended octanes in 4 cars of their choosing. Their intent was to discover if there was a difference in performance (MPG, acceleration, etc). You should read the article, but we note some of their interesting findings below.

Honda CRV

The Honda CRV required the lower octane. Car and Driver used the higher and found no real difference in overall performance. May as well stick to the recommended 87 octane.

BMW M5 Competition

The BMW M5 Competition called for a choice: 91 or 93 octane. So Car and Driver used both. While some results posted a relative difference, the numbers were too minimal to conclude 93 over 91 octane was cost effective.

Ford F-150 3.5 Ecoboost

ford f-150 with no engine knocking and proper octane

The Ford F-150 with the 3.5 Ecoboost is one reason we can not say higher than recommended octane NEVER makes a difference. Here’s a case where Ford’s engineers engineered their engine to accept higher octane. The F-150 on 87 octane did a 0-60mph sprint in 5.9 seconds. On 93 octane the result was over a half second quicker, at 5.3 seconds.

The dyno power on 87 octane was 360hp, whereas with 93 octane the horsepower was 380. That’s a decent 5% gain.

The quarter mile sprint benefited by 93 octane versus 87 octane with a half second gain. 14.5 seconds, versus 14.0 seconds using 93 octane.

Even miles per gallons (MPG) were better: at 75mph, 17.6 MPG with 93 octane versus 17.0 MPG with 87 octane. It’s still not cost effective to buy 93 octane over 87 for budgetary reasons, but no one is making the case for that.

It’s important to note here, these higher performance achievements are not due to 93 octane having more power or energy. They are mainly due to the engine being designed to handle 93 octane.

For my fellow 2021 F-150 family, our trucks recommend 87 octane. See what my truck performs 0-60 on 87 octane here and here. Also, this link shows you what it does for MPG on 87 octane after 1.75 hours of a commute in the DC area. For tips on how to drive a hybrid, click here!

Dodge Charger R/T

The Dodge Charger R/T, which from Car and Driver’s tests launched 0-60mph in 4.9 seconds, saw the same exact time whether they used 87 or 93. The Dodge Charger R/T recommends 89 octane fuel.

Are there any other possible benefits to higher octane?

A benefit to higher octane is that it can help compensate for compression loss due to knocking. Many people believe higher octane “burns off” built up carbon deposits, and that is not the case.

AMSOIL phrases the actual benefit perfectly:

"Deposits can reduce cylinder volume at top dead center, effectively increasing compression ratio.  This alone can lead to engine knock.  The deposits can also become hot spots that pre-ignite the mixture.  IN THESE CASES, a higher octane fuel helps resist engine knock and allows the engine to operate closer to it's normal conditions, rather than detuning to prevent engine knock."

The easiest way to begin to clean built up carbon deposits is by using additives and detergents found at your local auto parts store.

Who/what is AMSOIL?

Since AMSOIL is being referenced as an authority, let’s prove they are in fact an authority.

AMSOIL was the first synthetic motor oil in the WORLD to meet the American Petroleum Institute’s service requirements since 1972. AMSOIL is not my buddy from down the street at the local Exxon service station.

The Founder of AMSOIL, Al Amatuzio, was recognized in 1994 as the PIONEER of Synthetic Lubrication at the Lubricant’s Hall of Fame.

2 common octane misconceptions (per AMSOIL)

1. Higher octane and higher energy/power

A higher octane fuel is NOT higher energy just because it burns at a higher auto-ignition point. Some engines MAY benefit from a higher octane than is required or recommended. Those results vary from engine to engine and are based on design. It is not a universal rule of thumb.

2. Higher octane and higher quality

Higher octane does not equal higher quality. Quality will vary from brand to brand, who each add their own additives and detergents. These additives and detergents can just as easily be in the lower octane fuels as they would be in the higher octane fuels.


These principals apply to Hybrid engines the same as any other internal combustion engine.

We hope this helps many of you to understand fuels, octanes, ethanol a little better. I hope I answered “What is E85 gas?” and then some.

If you liked and appreciated this article, please let me know in the comment section below, subscribe to my blog, or look me up on social media. Maybe even hit a like button!

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