Is there an iphone app for tracking car miles and gas usage?

I drive my friends everywhere and i'd really like an easy way to track the amount i drive to see how much gas money i should ask for

Yes there's

You don't NEED an "app". Just READ the odometer and keep your receipts from the gas station.

Piece of paper and the odometer?

You need more than just gas. Insurance, tires, registration, repairs, purchase price. If I only have to pay your gas then I'd like to get rides too!
It's a bit of a calculation with variables. If you have a cheap second hand car that is economical on gas you should be charging at least 35 cents per mile or it is costing you to give rides.

The average person might spend $1500 a year on gas driving an average amount. A kid's insurance alone could easily be the same amount. One trip to the repair shop the same amount. Then the cost of the car divided by howmany years it will last (educated guess has to be made). Average car might pencil out th $1500 a year over 20 years life, $30,000 car.

I don't know about the app. Just seen too many young people use their car up and not be able to affordto repair or replace it.

Try searching in the app store. That's what I would have to do to give you an answer. Better you do it yourself.