Our local scrap merchant had to travel to the county recycling plant, 60 miles away.
On the way there he could only manage a steady 12mph, fully laden.
On the way back, he could manage a steady 16mph.
He placed 24 gallons of fuel in the tank ready for the round trip, thinking that this would be enough as the wagon managed to travel 8 miles per gallon. Unfortunately, a piece of metal pierced his fuel pipe at the start of the trip and the wagon started to lose 1 gallon of fuel per hour.
Luckily he only lost fuel when moving and he lost no fuel whilst unloading his scrap metal.