I once asked the Hertz supervisor at MRY to take my car back and see if the tank could take more gas. He came back and told me that he pumped another half a gallon. I was not suprised since a Nissan Altima's tank can hold 20 gallons, and the gas needle was a bit off of the full mark. In general, I prefer leaving with a full tank than trying to hit the needle exactly upon return.