I figure I can only get about 5.5 gallons in the darn thing, maybe 5.6 at the most. The filler tube below the cap is maybe 1.5 inches tall and you can only fill to the bottom of that without running it over. The fuel gage is another issue, only indicating distance in incemements from the bottom to the top of the tank. Totally ignores the tapered shape of the tank. I get about 60 miles to the first quarter tank, then maybe 40 to the second quarter, then about 30 to the third quarter tank. I've not yet determined the distance the final quarter would get me as the R3T is a heavy beast to push.