Mileage Keeper

Mileage Keeper tracks your vehicle's fuel economy, which helps you save money!
Mileage Keeper is simple to use. Just enter your odometer reading and fuel amount for each refueling, Mileage Keeper does the rest! Enter the total cost for each refueling, and Mileage Keeper will then also track cost/gallon (or litre) and the total amount spent on fuel for each vehicle. Add notes for each refueling to remind you of any differences from your normal driving habits. Didn't fill up your tank? Missed a refueling? No worries, Mileage Keeper can handle that too.
Fuel Economy can be calculated in either MPG(US), MPG(Imperial), km/l, l/100km, km/Gallon(US), km/Gallon(Imperial), or Miles/l. Fuel amounts can be entered in Gallons(US), Gallons(Imperial) or Litres. Distances can be entered in Miles or Kilometres. Use the device's "Settings" app to select your preferences. Mileage Keeper allows all combinations of units and will perform the conversions for you. All numbers, dates and currency will be displayed in your local style.
Data can be imported and exported by sending or receiving e-mails with standard .CSV files attached. See http://www.mileagekeeper.com for details.
Mileage Keeper supports multiple vehicles.
Best of all, it's free!