I usually rent from Avis and they would charge around $13.00 for under 75 miles if I did not have proof that I put gas in, even for 10 miles. Chances are that you would put in a gallon or two. I always buy gas if I can to avoid the fee. The only exception is when I'm in a real hurry. I also try to fill within about 20 miles of the rental because the gauge will still be at the full mark.