From my last car share reservation:
We have temporarily removed gas cards from all vehicles to prevent vandalism to our cars. If you need to fuel up during your reservation, please do so and send us the receipt for prompt reimbursement. To make sure the car is ready for the next member, just make sure the tank is at least 1/4 full at the end of your trip. We understand that this may create an inconvenience to you, and we apologize in advance.