From The PDA Initiative:
Tracks and stores your fuel consumption and mileage statistics, allowing you to make various mileage calculations. All of the common mileage measurements are included (MPG, L/100km, L/km). In addition, you can choose to export your data to a comma-delimited file. Graphing is provided to easier see your mileage statistics over time. Supports both US and British gallons. Over 20 statistics are available to tell you everything you need to know about your car's mileage performance.
Version 1.4.1 fixes an error for statistics with respect to L/100km mileage type.