Do I need to return a rental car with a full tank of gas?
Yes. The fuel tank will be full when you pick up your vehicle, so just make sure to return it with a full tank of gas. You will need to make a stop at a gas station near to your rental depot so you can just replace the fuel you have consumed before you drop the vehicle off to avoid paying for the refueling fees / service charges.
Car rental companies are very strict about vehicles returned without a full tank of gas. Customers who have not made any prior arrangements, and do not return the vehicle with a full tank will be charged an additional fee. Take note that these companies can detect when a fuel tank is not full or part-full. You can avoid this either by choosing and paying for the pre-purchase fuel option or simply refueling it to the same level you received it when you picked up the vehicle.