pyFuel

is very simple (the simplest you can imagine) app, that will help you to track your fuel expenses and your car fuel consumption.

I'm assuming your car doesn't have a built in computer. In other case you don't need pyFuel.

With pyFuel you can also calculate trip costs, based on average fuel consumption from last refuelings.

I hope it'll be handy and useful. Don't hesitate to ask questions, report bugs or give any sugestions. You can do it at sourceforge.net.