The car owner pays for all the fuel that goes into the vehicle. They are reimbursed 25 cents for every kilometre the borrowers drive.
If a borrower needs to fill up during their booking, they use the fuel card that's stored in the glovebox of the car.
Any fuel the borrower purchases on the card is charged to the owner in their monthly invoice, but this is offset by the payment of 25 cents for every kilometre that borrowers have driven.
The cost of fuel for the average medium car costs between 7c and 11c a kilometre, and the cost of servicing and tyre wear is approximately 6c and 12c a kilometre (source: RACV running costs guide). So your distance income should more than compensate the owner for the additional running costs of their car.