Best I have seen was 26, this was heading back up north from Florida about 4 years ago. Fiance took over for a while and she woke me up to let me know we would be home in 2 hours and if anyone needed a restroom break, etc. Well we stopped at the 95/301 interchange in VA, fill up was like 13.2 or 13.4 gallons. She drove 342 miles IIRC. I was like WTF, I asked if she tailgated an 18 wheeler, how fast was she going, she said not tailgating and doing about 65-70 with cruise Best I have seen with me driving was 22.5, and I average 15.9 rural/suburb driving.