1998 Mercedes 2.3 liter supercharged coup; 26mpg = 28 us cents per mile (gasoline is expensive here).
2000 Mitsubishi 4-door 'Carisma' sedan, 1.9 liter turbodiesel, 38mpg, 18 US cents per mile (Diesel is expensive too, but a lot cheaper than gasoline).
Those are real numbers, I calculate and reset the odometer each time I fill fuel.
Tractor... I think that will be in gallons per mile.