I based my statements off my 2001 Toyota Tundra with a 26.5 gallon tank - fuel light comes on at about 21 used gallons. In my old Honda Accord - I still had about 50-75 miles til empty, so that was about 3-4 gallons left. My estimates may be off, but either way, there's still a couple of gallons left - and at $4+ gallon, I just doubt you're saving that much (again, unless you're returning it COMPLETELY empty).