Roger Hoy, professor and director of the Nebraska Tractor Test Lab, University of Nebraska-Lincoln, calculates how a difference in ratings can translate into dollars saved:

“To create a simple example, let's assume that we have two 200-hp tractors operating at rated engine speed and delivering all of their available power — one operating at 17 hp-hr./gal. and one operating at 18 hp-hr./gal. For the tractor with 17 hp-hr./gal., we divide 200 by 17 and find a result of 11.76 gal./hr. Similarly, we find the 18 hp-hr./gal. tractor to use 11.11 gal./hr., or a difference of 0.65 gal./hr. If we assume that the tractor will be used for 500 hrs. each year and ag diesel has a cost of $4.00/gal., the annual difference in fuel costs between these two tractors is $1,300.”