I'm gonna go ahead and let the Maxima stand because it's both impressive and believable. But, I'm going to implement a new rule: 4 gallons minimum. Why? Couple reasons. Because it's too easy to find a place where you can burn a gallon or two with very favorable (and unrealistic) conditions. Also because the margin for error is much greater as the amount of fuel goes down. We can measure miles fairly accurately with the odometer (as long as you haven't changed your tire size or gearing), but we're at the mercy of the fuel pump auto-shutoff for our fuel fill readings.

For example, if we put an extra .1 gallons in the Nissan above, the mpg goes from 37.02 to 34.8, a very significant difference. If we were talking 5 gallons @ 37 mpg, that would be 185 miles. Adding .1 gallons of fuel brings it to 36.2. Still fairly significant, but it's less than 1 mpg, and .1 gallons is probably a worst-case error.