Calculating Diesel Fuel Costs for a Commercial Fleet

Last updated July 2, 2026

Diesel fleet fuel cost calculation follows the same fundamental approach as gasoline fleet calculations but requires using diesel-specific pricing, which in 2026 typically runs $0.40 to $0.60 per gallon above regular gasoline, and diesel-specific fuel economy figures, since diesel engines typically achieve 25 to 30 percent better fuel economy than comparable gasoline engines due to higher energy density and more efficient combustion characteristics. A fleet of diesel delivery trucks averaging 12 MPG driven 35,000 miles annually each consumes approximately 2,917 gallons per truck, and at $4.50 per gallon diesel pricing, annual fuel cost per truck reaches approximately $13,125.

The diesel premium per gallon is frequently offset by the superior fuel economy diesel engines provide, making cost-per-mile rather than cost-per-gallon the more meaningful comparison metric for fleet planning purposes. A diesel truck achieving 12 MPG at $4.50 per gallon costs $0.375 per mile in fuel, while a comparable gasoline truck achieving 9 MPG at $3.95 per gallon costs $0.439 per mile, meaning the diesel option remains more cost-effective on a per-mile basis despite its higher per-gallon price, a calculation that becomes increasingly favorable for diesel as annual mileage increases and the fuel economy advantage compounds across more miles driven.

The calculation shows diesel fleet costs using cost-per-mile rather than cost-per-gallon as your primary comparison metric, since diesel's higher price per gallon is typically offset by meaningfully better fuel economy. This per-mile comparison provides the accurate basis for fleet fuel budgeting and for evaluating whether diesel or gasoline vehicles offer better total fuel economics for your specific fleet's mileage patterns.