Cost per mile: fuel math for an owner-operator

Fuel cost per mile is the simplest important number in trucking: the price of a gallon of diesel divided by the truck's miles per gallon. At the DOE number for the week of Oct 5, 2026, $6.199 a gallon, a truck getting 6.5 mpg spends about 95.4 cents a mile on fuel. Everything else in an owner-operator's fuel math is a variation on that one division.

Why mpg is everything

Because cost per mile is price divided by mpg, a small change in economy moves the number a lot. Hold the price at $6.199, the DOE number for the week of Oct 5, 2026, and run it at three efficiencies. At 6.0 mpg the fuel cost is about 103.3 cents a mile. At 6.5 mpg it is about 95.4 cents. At 7.0 mpg it is about 88.6 cents. A truck one full mile per gallon better spends about 14.7 cents a mile less on fuel, which over a 500-mile haul is about $73.79. Over a year of running, that is real money.

The chart above is the DOE number restated as fuel cost per mile at the 6.5 mpg reference. It is the same price the number page carries, in the unit an operator actually plans in. The diesel cost per mile page tables this week's figure at every fuel economy from 5.5 to 8.0 mpg and in each of EIA's regional breakouts.

The 6.5 mpg reference

This site uses a stated 6.5 mpg reference on every per-mile figure. It is a plain mid-fleet figure for a loaded Class 8 truck, chosen so one week compares cleanly to the next, not an estimate of any particular rig. Your truck differs with spec, load, terrain and weather. A reefer pulling a grade in winter will do worse; a light load on flat interstate will do better. Take the reference number and scale it to your own measured economy.

Fuel is a big slice, not the whole pie

Fuel feels like the whole cost when the pump is high, but it is one line among several. The American Transportation Research Institute, which tracks what it costs to run a truck, put the 2025 average at $2.336 a mile in its 2026 Operational Costs of Trucking update (July 2026), $1.854 of it excluding fuel. That leaves fuel at about 48 cents a mile, roughly a fifth of the total, in a year when the DOE number averaged $3.660 a gallon. When diesel runs higher, fuel takes a bigger slice of the same mile.

The other lines in ATRI's per-mile total are worth knowing, because they frame where fuel sits: driver wages and benefits, truck and trailer payments, repair and maintenance, insurance, tires, and tolls. ATRI found every one of them rose in 2025, with tolls and repair and maintenance up the most. Fuel is the one that swings hardest week to week, which is why it draws the most attention, but it is not the one that most decides whether a truck runs profitably over a year.

Over a year the mpg gap is real money

The per-mile numbers look small until you run them out. A truck covering 100,000 miles a year at $6.199 diesel (the week of Oct 5, 2026) and 6.0 mpg burns about $103,300 in fuel. The same truck at 7.0 mpg burns about $88,600. That is roughly $14,700 a year riding on one mile per gallon at that price. That is before a single change to how the truck is driven or specced. When diesel is higher the gap is wider still, which is why fuel economy is the lever operators come back to.

The deadhead caveat

One thing the pump math hides. Fuel burns on loaded miles and empty miles alike, but only loaded miles earn. A run that deadheads a long way to the next load costs fuel on the empty leg with no revenue against it, so the true fuel cost per paid mile is higher than the price-divided-by-mpg figure suggests. If 15 of every 100 miles run empty, divide the per-mile figure by 0.85 to get fuel per paid mile. When you price a lane, the empty miles are part of the fuel cost even though they never show up on a rate confirmation.

Monday Diesel turns the DOE number into cents per mile at a stated reference so the weeks compare. It does not estimate your truck's economy for you and it does not advise on when or where to fuel.

Monday Diesel is a free weekly read of the DOE diesel number and what it does per mile. Built entirely from EIA's public data, in your inbox before dispatch, one email a week.