Ethanol reduces your miles per gallon (mpg) compared to gasoline that contains no ethanol, based on the energy output of ethanol vs gasoline. This calculator compares value based on price per gallon of gas.
For example, if normal non-ethanol gas is $3.499, then for E85 to provide more miles per dollar the price must be less than $2.482; E15 would give more miles per dollar when less than $3.319; and E10 would give more miles per dollar when less than $3.379)
So buy the lowest Octane that your car is rated for. Anything higher will not hurt your car but also will not help your car, so you would probably be wasting money. Most US cars take 87 octane, except for luxury brands like Cadillac, BMW, Mercedes, etc that often require 91 octane. (or 85 and 89 respectively in high altitude Mountain areas)
You have 2 choices if the price at the pump is within pennies of the calculated best price.
GasPumpr calculations are purely informational and economical. Other online resources show the pros/cons of ethanol effects on your engine, along with additional environmental benefits, or even the political effects of ethanol subsidies. Your actual miles per gallon may vary slightly from this generic calculation. See the published mpg and E85 mpg of your car at fueleconomy.gov
Even though this calculator is displayed in US-dollars, the calculation is the same for any currency. Just ignore the dollar sign and the results are fine if you are trying this calculation in Mexico, Canada, Europe, etc...
This site was designed for mobile use for easy access from your phone.
Intial thoughts were generated by a Consumer Reports article "The great ethanol debate", January 2011