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.

Read more about returning your rental car.

For example:

Oliver pre-purchased a tank of fuel

Oliver heads back to the car rental depot to return his vehicle to Vancouver Airport (YVR). Coming straight from the city, Oliver knew beforehand that he would not have time to refuel the vehicle. So to avoid the hassle of having to fuel up the car, he decided to prepay the gas when he picked up the car. The vehicle only has half a tank of full when he drops it off at the depot. But since he already pre-purchased the fuel, there will be no additional charges. He will also not receive any refunds for the unused fuel.