While we did not have equipment to measure propane flow, Lehr vice president of engineering David Kostka shared his fuel consumption data. At 3,300 rpm, the 5 hp model burns pro-pane under load at a rate of 0.18 gph, Kostka said. At our speed of 4.5 mph at 3,300 rpm, that equates to an astonishing 24.3 mpg. As speed increases, mileage drops sharply. At 4,600 rpm, for example, the speed was 6.2 mph, and with Kostka’s burn rate of 0.5 gph, that equates to a more believable 3.1 mpg.