does ethanol reduce you “mpg”?

Yup. It contains less energy per volume than gasoline.

Bummer, huh?

seems like I’m losing easy 10% maybe 20%“mpg”–my metro reliably gets 40-44 mpg—but now w/ethanol added to our gas in my area i’m down to 35 mpg------w/my buick i’ve dropped from 25mpg to less than 20…

For E10, the rule-of-thumb is about 3% or so drop in mileage. Are you using gas with more than 10% ethanol? IIRC, pure ethanol gets about 30% lower mileage (lower energy content), so 10% would be about .3 * .1 = 3%. If you’re running E10 and getting 10 to 20% lower mileage, I wouldn’t blame the gas… something else is wrong.

if it was only with 1 car I’d agree but w/ 2cars being affected I’m not sure-----E10 is correct for my area.

Ethanol gas is called oxygenated gas. Which means it contains oxygen. So when it’s burned this extra oxygen is detected by the O2 sensors. This extra oxygen causes the computer to add more fuel to compensate for this extra oxygen. Which reduces the fuel mileage.


Thanks, I’m going to fill up my metro and see if anything improved since I tuned it up the other day.

Tester is 100% correct. This “oxygenated fuel” stuff all started back when most cars were carbureted and tended to run a little rich, especially at idle. The “oxygenated fuel” helped out reducing the CO emissions that had reached dangerous levels in many cities. Fuel injection, oxygen sensors, catalytic converters and computerized engine controls has virtually eliminated CO from car exhaust but the need to extend our fuel supplies any way possible remains. If the ethanol was removed, it would have to be replaced with imported oil. We, as a nation, can no longer afford that. With ethanol, your fuel dollars stay in the United States instead of enriching foreign countries. Also, the ethanol industry has been given 10% of the motor fuel market and they are not going to give it up.


There are a lot of factors.  First while ethanol is usually 5% alcohol it may be higher.  In a few cars you might get slightly better mileage with ethanol due to differences in octane, but most cars will give you less mileage since ethanol has less energy per unit of volume than gasoline.

Now 2 weeks later I can report that getting “e10” gas out of my car[s] and using “gulf” w/ no ethenol my milage is back to nornaml!!Last 2 tanks in the metro are back to a lil over 40 mpg!

Thank you for the follow up post. It’s always good to have our consensus confirmed in application.

Happy motoring.

The Persian GULF Oil Company appreciates your business…

Are you being delightfully funny or is that “gulf’s” formal name? Whichever , my 2 cars like their gas better than all the other options in my area!