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Does Ethanol Reduce Your Gas Mileage?


I've always been interested in getting the most out of my vehicles from a fuel efficiency standpoint.

The advertisement from a local chain of filling stations for ethanol treated gasoline, also known as E10.

The advertisement from a local chain of filling stations for ethanol treated gasoline, also known as E10.

America's Fuel

A local gas station chain markets their regular unleaded gasoline as ethanol enhanced. The use of the word “enhanced” is curious because it implies that there is some benefit or advantage to choosing this gasoline over other available products. Messages on the pump further add that this is “America’s Fuel” and that it may contain up to 10% ethanol. This ethanol modified product is commonly called E10.

As an alternative, the chain also offers an ethanol free 87 octane product called PureMax, which is an interesting name in its own right. Another gas station just down the street calls their ethanol free fuel "Pure Gas" and proudly advertises that it will improve your gas mileage by 25% over ethanol grades. Pure gas is typically more expensive than E10 with the same octane rating. For example, during my last visit, the E10 cost $3.299 per gallon while the PureMax was listed at $3.679 per gallon. Since I ended up buying 11 gallons, the E10 saved me around $4. At first glance, the obvious enhancement imparted by the ethanol addition is to the upfront cost of filling your tank.

A sign at a local gas station touts the supposed benefits of ethanol-free pure gas.

A sign at a local gas station touts the supposed benefits of ethanol-free pure gas.

Based on the unit price it seems obvious there is an initial savings benefit to choosing the E10 ethanol treated gasoline. However, do you really see a financial benefit when all is said and done? Ethanol has about 25% less energy content than gasoline, so adding this substance dilutes the ability of the fuel to fire the pistons and gives your engine less bang for the buck. Consequently, due to this energy density reduction, there is a chance you will actually get fewer miles per gallon if you choose the ethanol enhanced fuel over an ethanol free grade like PureMax. Maybe the banner that proclaims you can save 25% on gas mileage is right.

So, does the ethanol infused E10 provide a financial enhancement over an alcohol-free option like PureMax just by being cheaper or is the upfront savings lost due to the inferior gas mileage of the fuel? To get to an answer, we need to calculate the number of miles per dollar of gasoline purchased, or miles per dollar (MPD). Just for fun, I decided to conduct an experiment to determine the MPD of both the E10 and the PureMax fuels to see if ethanol gasoline can truly be called enhanced or if the "No Ethanol" sign is right after all.

Ethanol Enhanced E10 Versus PureMax Pure Gasoline

Gas nozzle for PureMax, a pure gas fuel offered by local filling stations

Gas nozzle for PureMax, a pure gas fuel offered by local filling stations

To evaluate the effect of ethanol on miles per dollar or MPD I decided to run a little study using my own vehicle. I drove my 2008 Subaru Forester for several weeks using the ethanol enhanced 87 gasoline and recorded the mileage and fuel consumption. Then I switched over to the Puremax ethanol free and monitored the same information. I ran the results through a statistical analysis called a two-sample t-test to determine if there truly was a performance difference between the two fuels. Finally, I calculated the miles per dollar.

During the experiment, I tried to keep my driving habits and patterns as consistent as possible. The driving represents a mix of highway and city driving, mostly on my commute to and from work. If I took a long highway trip on a certain tank of gas, I discarded that tank from the study.

Table 1 below shows the results for the E10 gasoline. The average gas mileage came out at 24.2 MPG and based on the recent cost of $3.299 per gallon; this gives a miles per dollar or MPD of 7.33.

Table 2 contains the PureMax test results and shows the gas mileage at 25.8 MPG. With the recent cost per gallon of this fuel at $3.679 it ends up having an MPD of 7.01.

These results show that you can see a gas mileage boost of approximately 7% by using the pure gasoline instead of the E10, but based on current prices you end up getting penalized financially due to the higher cost as shown by the 4% drop in miles per dollar.

Table 1 - E10 Gas Mileage Results






























Table 2 - PureMax Gas Mileage Results


























The price per gallon for ethanol-free Puremax.

The price per gallon for ethanol-free Puremax.

The Bottom Line

My experiment showed that using ethanol enhanced E10 fuel instead of the ethanol free PureMax reduced my MPG by 6.2%, from 25.8 to 24.2 miles per gallon. However, because of its higher cost, the PureMax actually delivered 4.4% less MPD than the E10, 7.01 versus 7.33 miles per dollar, and turned out to be the worse choice from a cost perspective.

This financial benefit, however, depends on the price difference between the two grades. As the pure gasoline price approaches the E10 cost, a crossover point is reached where it actually becomes the better value in terms of MPD. With the results of this study, I came up with a guideline called “The 20 Cents Rule” that is easy to remember. It states that if the ethanol free option costs 20 cents or more per gallon than the E10 than go with the E10, but if the difference is less than 20 cents then pure gas is the better value.

The other thing I learned is that you can't always believe what you read on advertisements since the pure gas delivered only a 7% increase in MPG instead of the "up to 25%" written on the banner. However, because of the lower overall cost of the ethanol enhanced E10 the ethanol does appear to provide a financial "enhancement" to the consumer.

Prices for the ethanol treated varieties of gasoline.

Prices for the ethanol treated varieties of gasoline.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2012 theframjak


P ALLAM on December 22, 2019:

No environmental or mechanical benefits announced with it's introduction here in UK. Suppliers will benefit - reduction in potency results in increased consumption.

Did'nt mention that anywhere did they ?

theframjak (author) from East Coast on November 15, 2019:

Thanks for your comment Michael. The t-test shows there is an actual difference between the two fuels and that they are not part of the same population.

Michael Czajka from Sunshine West, Melbourne, Victoria, Australia on November 15, 2019:


Fuel dilution of oil by ethanol reduces the lubricating efficiency and wear protection of the engine. That's yet another reason why the fuel efficiency drops.

Once the oil is affected any future test will also suffer from the same problems (until you change the oil... and maybe even longer than that?). Fortunately the gasoline test was run first... so any changes to the oil by ethanol wouldn't have affected your result.


P.S. What did your statistical two sample t-test tell you about the power of your results?

Michael Czajka on November 14, 2019:


Wikipendia says that the energy equivalent of 1 unit of gasoline is 1.5 units of ethanol... which goes a long way to explaining why you got a 6.2% reduction in fuel efficiency.

I apply a 10c rule to the fuel in Australia... which is roughly 6.2%. Thanks for confirming that the actual fuel efficiency decrease is more than the theoretical estimates would have you believe.


Marc J Rauch on April 28, 2019:

There is no such thing as "pure gasoline." Gasoline contains from 150 to 1,000 different ingredients.

The author is correct in his/her evaluation of the ethanol-gasoline blends.

Daniel H on November 23, 2018:

Too bad this blog is sooo old.

I have been wondering why, when MTBEs and Alcohol were introduced in Massachusetts, but not in Maine, why when driving in Maine on locally purchased non-alcohol added gasoline, my 90 Voyager showed 24 miles per gallon on average, and when I came to Massachusetts where alcohol (10%) was present, my computer consistently showed me at 17 mpg.

Now some years later, I note black mold on the side of my car near the fill point - what is it living on - never had this when I was younger (no alcohol in fuel). Now house roofs have black streaks of mold and lichens even are growing on roofs!

Could the fuel be quietly increasing the tax part of the fuel? ....and why is the black and green mold all over everything so prevalent now in 2018?

We don't need alcohol to fake octane as the computers can accomplish the same thing as they have as wide a range of combustion control as needed - and just think, we're clearly going to become the victims of all that mold!

stephen leonhard on August 14, 2018:

Unless the real world has changed radically since I earned my degree in chemistry adding alcohol to gasoline is yet another of the governments BAD ideas.

Alcohol has about 30% less energy per gallon and is highly hydroscopic drawing water from the atmosphere which leads to all manner of fuel system problems.

Stefan on June 18, 2018:

Hell yes it does and also will destory your car engine and other components. With E10 Gas i was getting 15city 19highway, since driving an hour to a station that offers E0 Ethanol free gas, i got my MPG completely. Now i am 21city / 27 highway. Huge difference!!!!!

We all need to take a stand against this shit! We work hard enough to buy are cars, not to let them get destroyed by greedy and illogical federal regulations

theframjak (author) from East Coast on March 16, 2018:

Yes, these are all valid comments. It would be best to perform the study with several different types of vehicles. This article offers just a general guideline.

T. Saroch on February 24, 2018:

This basically true(20 cent rule) , but would it not change according to the vehicles mpg. If the increase or decrease isa certain percentage. A 7% change on a vehicle getting 10 mpg would be different than on one getting 45 mpg. Also in a truck pulling a load, would not the performance change?

Tom on August 07, 2017:

MTBE vs Ethanol vs Tetra-Ethyl Lead -- all used to oxygenate gasoline -- all are used to "lean out" your fuels combustion- which when pure gasoline is used is too high causing pinging.

country boy on April 13, 2017:

That answers my question why my vehicle will do 4 mpg better without the ethanol.

Now I know why my lawn equipment won't start after sitting for months. Mechanics have informed me to use pure gas.

theframjak (author) from East Coast on March 02, 2015:

Hi Dressage Husband, Thanks for reading. I'm glad to hear you liked it. You bring up a good point with the long term effects of E10 use on engine components. I'm sure this also has financial consequences on the overall use of this fuel compared with the pure gas alternative. Thanks again for stopping by.

theframjak (author) from East Coast on March 02, 2015:

Hi purl3agony, thanks so much for reading my HOTD. I never thought I would get one, but it finally happened! I'm glad you found it to be useful.

theframjak (author) from East Coast on March 02, 2015:

Hey drpennypincher, thanks for reading. You're so right, there are a lot of other factors that can come into play and affect the results, which makes these experiments so challenging. Thanks again for stopping by.

theframjak (author) from East Coast on March 02, 2015:

handymanbill, thanks so much for reading and sharing the interesting information about ethanol fuel. I had heard about this in regards to my lawnmower but didn't consider that it would also be true for my car.

Stephen J Parkin from Pine Grove, Nova Scotia, Canada on March 02, 2015:

I really liked this Hub and the way you derived the actual miles per dollar spent. This is the only criteria for most users to be concerned about. The only factor not mentioned is any effect on the life of engine components and servicing costs. I am not sure what the long term affect of using ethanol would be if this was taken into account.

Donna Herron from USA on March 02, 2015:

I appreciate you collecting this data and doing the analysis for all of us. I know if I want to be a responsible driver, I should be noting and charting my gas consumption, but I never do. Thanks for this easy to understand comparison of the potential value of ethanol gas. Congrats on your HOTD!!

Dr Penny Pincher from Iowa, USA on March 02, 2015:

I like how you did experiments and presented your data. Hard to argue with that. The difference in mpg is subtle enough that small differences in driving, such as having a passenger or a bit of extra city driving can make it hard to see the difference in mpg between pure gas and ethanol. But collecting data from multiple tanks makes it easier to see the trend. Nice work.

Bill from Greensburg Pennsylvania on March 02, 2015:

what is really an interesting fact also not even talked about here. Is that the shelf life of Ethanol gas is far less then the shelf life of regular gas. That is why in cools weather you should keep your Tank full. If you do not then the gas with Ethanol will possibly have water condensation in it. Also it is hard on your car engine.

theframjak (author) from East Coast on April 17, 2013:

Thanks for reading m. I think our two rules are close enough to support each others finding.

m on April 07, 2013:

Good post. I did a strictly numeric analysis that came up with a similar result. Ethanol has 34% less energy density than gasoline. My break even number at an E10 price of $3.41 is $3.53 for pure gasoline so it is closer to a 15 cent rule in a purely theoretical world. Either way, wohosr is right and that doesn't even include the increased cost of corn tortillas.

theframjak (author) from East Coast on March 16, 2013:

wojosr, you raise a good point. Like so many other things, there are often underlying costs associated with things that are not apparent at first glance or get buried. Thanks for reading.

wojosr on March 14, 2013:

Based on your test and my personal mpg records when gas was still available in addition to E10 it shows that rather than reducing the amount of oil the country is using we are using the same or more than after the gov. required the use of ethanol as an additive to gas. Oil is delivered to the refineries by pipeline whereas the ethanol uses trucks to bring corn to ethanol refinery then ships the ethanol to the refineries to add to gas which consumes fuel and then we experience lower mileage which means we use almost the same amount of gas as before E10 and the additional fuel required to produce and deliver ethanol actually increases the oil needed in the country.

theframjak (author) from East Coast on March 12, 2013:

Monis Mas, Thanks so much for reading and thanks for the enthusiastic response. Hopefully, your husband will also find it interesting.

theframjak (author) from East Coast on March 12, 2013:

toknowinfo, thanks for reading and thanks for the complement. I'm glad you enjoyed the articles.

Agnes on March 11, 2013:

Awesome hub, I am sharing with my husband!

toknowinfo on March 10, 2013:

Great article. It explains why the oil companies use ethanol, which is a corn derivative, and more expensive to produce than oil. Knowledge is power, so thanks for the great info. Voted up and more and sharing and putting it on twitter.

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