Diesel box truck vs gas: what each costs per mile and when each wins

Diesel or gas is one of the biggest choices in buying a box truck, and most advice on it is opinion. This guide works from numbers instead: this week's U.S. fuel prices from the Energy Information Administration, the miles per gallon that rental fleets publish for their own trucks, and the engines makers actually offer. Then it shows which way the math tends to lean for different kinds of work.

Which box trucks run on diesel?

Both fuels are common, and the split follows size more than brand. Among the published rental specs we checked:

SOURCE:Budget Truck Rental, OCT 2026;Penske Truck Rental, OCT 2026;U-Haul (page snapshot 2026-09-28, Internet Archive), OCT 2026;U-Haul (page snapshot 2026-09-28, Internet Archive), OCT 2026;Penske Truck Rental, OCT 2026;Budget Truck Rental, OCT 2026

Makers offer both. Isuzu sells its N-Series in gas and diesel versions, and its F-Series runs the Cummins B6.7, which Isuzu describes as a six-cylinder diesel. Freightliner lists a gasoline option, the Cummins B6.7 Octane, for its M2 106. International offers its MV Series with the B6.7 and L9 engines.

SOURCE:Isuzu Commercial Truck of America (Internet Archive snapshot), OCT 2026;Isuzu Commercial Truck of America (page snapshot 2026-02-16, Internet Archive), OCT 2026;Freightliner, OCT 2026;International Motors, OCT 2026

Fuel cost per mile: diesel vs gas this week

Fuel cost per mile is the price per gallon divided by miles per gallon. Here it is with EIA's U.S. averages for the week of September 28, 2026 and each fleet's published mpg:

Two things show up. First, diesel cost $1.92 more per gallon than gasoline that week, so a diesel truck has to get much better mileage to match a gas truck per mile. Second, the fleets' estimates for diesel and gas 26 footers overlap: Budget lists 8 to 10 mpg for its diesel and U-Haul 8 to 10 for its gasoline truck. At those numbers, the gas truck's fuel costs less per mile this week.

That does not settle it. These are rental fleet estimates for mixed use; a diesel truck hauling heavy freight on the highway, driven well, may beat its rental estimate, and the price gap between the fuels moves from week to week. The point of the table is the method. Put in your own mpg and your local price, and the answer is yours. The trip fuel cost calculator and box truck cost per mile calculator do it for you.

SOURCE:U.S. EIA, Gasoline and Diesel Fuel Update, OCT 2026

What else separates diesel and gas box trucks

Fuel is one line in the cost of running a truck. The others to compare, model by model:

• Purchase price. Get quotes on the same chassis with each engine where the maker offers both.
• Maintenance. Ask the dealer for the service schedule and parts costs for each engine, including any emissions equipment.
• Payload. Engine and fuel system weight come out of payload. Compare published payloads, not just ratings.
• Range. Tank size times mpg. Budget's diesel 26 ft truck carries a 50 gallon tank; U-Haul's gas 26 footer has 60 gallons.
• Resale and life. Ask what similar used trucks of each type sell for in your area. Our used box truck guide covers what to check.

SOURCE:Budget Truck Rental, OCT 2026;U-Haul (page snapshot 2026-09-28, Internet Archive), OCT 2026

When diesel tends to make sense

• High annual miles. The more miles, the more any mpg advantage adds up.
• Heavy loads. Dense freight near the payload limit, where torque and engine durability matter.
• Larger chassis. Some medium-duty chassis, like Isuzu's F-Series, come with a diesel engine; see medium duty box truck.

When gas tends to make sense

• Lower miles. Local routes where the truck sits part of the day.
• Lighter boxes. 10 to 20 ft trucks carrying bulky, light freight.
• Lower purchase cost and simpler upkeep, if the dealer quotes confirm it for the model you are considering.

Electric as a third option

Battery-electric box trucks are on the market too: Isuzu lists an N-Series EV. Range, charging and price are different questions again; our electric box truck guide covers them.

SOURCE:Isuzu Commercial Truck of America (Internet Archive snapshot), OCT 2026

Fuel and the loads you book

Whatever the fuel, every empty mile is paid at full price. On a box truck hauling for brokers, the fuel decision matters less than the miles you run without freight. Our box truck sizes chart and the truck size calculator help match the truck to the work.

SOURCE:U.S. EIA, Gasoline and Diesel Fuel Update, OCT 2026;U-Haul (page snapshot 2026-09-28, Internet Archive), OCT 2026;U-Haul (page snapshot 2026-09-28, Internet Archive), OCT 2026;Budget Truck Rental, OCT 2026;Budget Truck Rental, OCT 2026;Penske Truck Rental, OCT 2026;Penske Truck Rental, OCT 2026;Isuzu Commercial Truck of America (Internet Archive snapshot), OCT 2026;Isuzu Commercial Truck of America (page snapshot 2026-02-16, Internet Archive), OCT 2026;Freightliner, OCT 2026;International Motors, OCT 2026

Questions box truck owners ask

Q-01Do box trucks use diesel?

Many do, and many do not. Among rental specs we checked, Budget's and Penske's 26 ft trucks run diesel, while U-Haul's 26 ft truck and the 16 ft trucks from Penske and Budget run gasoline. Makers offer both in box-truck chassis: Isuzu sells gas and diesel N-Series trucks, and Freightliner lists a gasoline engine option for its M2 106.

Q-02Is a diesel or gas box truck better?

Neither in general. Diesel suits heavy loads and high annual miles where its mpg and engine life can pay back the higher fuel price and purchase cost. Gas suits lighter boxes and lower miles, with cheaper fuel per gallon. Run your own miles and loads through a cost-per-mile calculation before you choose.

Q-03How many mpg does a diesel box truck get?

Rental fleets publish estimates: Budget lists 8 to 10 mpg for its diesel 26 ft truck and Penske up to 13 mpg for its diesel 22 to 26 ft box. Real mileage depends on load, terrain, speed and idling. Our box truck mpg guide explains how to measure your own.

Q-04Why is diesel more expensive than gasoline right now?

EIA's weekly survey shows on-highway diesel averaging $6.382 a gallon and regular gasoline $4.465 for the week of September 28, 2026. Prices move weekly and the gap between them changes, so check the current numbers before running comparisons. EIA publishes regional averages too.