Something else to consider; modern cars have the fuel pump IN the gas tank, using fuel as coolant for the pump. Letting the gas get too low will stress the pump... do that too often and you may need a new gas pump, which means (A) a lot of labor costs to replace the pump, or (B) a new gas tank (or a referb if you're lucky). My advice: don't press your luck, stop and refuel ASAP.