Gas with or without 10% ethanol?



When using 91 or 94(Sunoco Ultra) octane gas with 10% ethanol my 2007 Lexus gets 15% less gas mileage.

Is this normal?


Yes, it’s perfectly normal. Ethanol does burn cleaner than gasoline, but it has about 30% less energy than gasoline. Therefore, the ethanol mixture is less efficient and you get poorer mileage.


Absolutely! Ethanol reduces fuel mileage in all vehicles, and since it isn’t cheaper than regular it’s sort of a rip-off, don’t you think?


I’m going to send my legislators our opinion & hope to get something going to force posting at the pump when the gas contains ethanol.


Although ethanol has 30% less energy than gasoline, the loss in energy for the E-10 mixture is only 10% x 30% = 3%. A 3% reduction in gas mileage would be only 1 mpg for a car that normally gets 33 mpg. This is too small to measure outside a laboratory. For E-85, which is 85% ethanol, the reduction in fuel mileage is 20% to 25%.

At present, when you factor in the tax breaks that ethanol enjoys, you get more miles per dollar from gasoline than from ethanol. However, it makes sense to subsidize the industry just enough to make it a viable alternative to gasoline in case the latter becomes impossibly expensive.

My current cars are designed to run on unleaded regular which is 87 octane most places or 85 octane at high altitude (Rocky Mountain states). When I have a choice, I buy E-10 provided it is at least 3% cheaper than straight gasoline. At today’s prices, the necessary price break is about 10 cents per gallon.

Some cars, that were designed to run on premium, can tolerate lower octane fuel. However, performance, which includes gas mileage, is degraded. Usually, the gasoline portion of E-10 is regular, not premium, and the mixture’s octane falls between that of regular and premium. If the E-10 you have been using is like that, it may explain why your Lexus gets such poor mileage with it.