The price of diesel does not set your freight fuel bill. Three numbers chosen by the carrier do: the base price peg, the assumed miles per gallon (MPG) and the rate table [2][3]. Change any one of them, and the same diesel price buys a vastly different bill.

The big picture:

The federal diesel index is the one piece nobody controls.

The Energy Information Administration (EIA) posts the highway retail price each week. Carriers tie their tables to that public list [1][2]. Everything else is a choice.

A per-mile plan takes the current diesel price, drops the base peg, and divides by the assumed MPG [2]. At $4.25 diesel, a $2.50 peg and 6.5 MPG, the fee is $0.269 a mile. That adds $322.80 to a 1,200-mile load [2].

What strikes me here is the total lack of a referee. No government rule sets the charge. Each carrier builds its own baseline, MPG and tier setup [4].

The math sits in plain sight on the carrier’s site. Yet buyers rarely read it after they sign. A heavy route mix multiplies this math, turning pennies per mile into a massive cost across a fleet.

By the numbers

  • $5.60/gallon — EIA diesel price: The highway retail price in the agency’s latest May 2026 report. Carriers use this list to set their pegs [1].
  • $0.269 per mile — Worked fee: What one per-mile table pays at $4.25 diesel, a $2.50 peg and 6.5 MPG [2].
  • 47 cents per mile — Peg sensitivity: The exact same formula at a $4.00 index, a $1.20 peg and 6 MPG. The peg and MPG drive the cost, not just the market price [3].
  • 22% to 23% — Banded table: How a less-than-truckload (LTL) carrier prices fuel. A price of $3.00 to $3.09 maps to a 22% fee on the base rate. Hitting $3.10 sparks a 23% jump [4].

What I’d watch:

The folks closest to this are not guessing future diesel prices. They are re-reading the sheets they signed. I am watching teams check four specific levers.

  • The peg: A lower base peg raises the fee at every single diesel price [3]. Two carriers can quote the same base rate but bill very differently because one drops $1.20 and the other drops $2.50 [2][3].
  • The MPG guess: A low MPG figure makes the fee climb faster than the real fuel cost [3]. The gap between a carrier’s guessed MPG and its real fuel use is where the margin hides.
  • The banding: Tiered tables step up when diesel crosses a set line [4]. I would want to know where those edges sit against today’s index before a renewal.
  • The audit line: Fuel runs 20% to 30% of a carrier’s running costs [2]. Leaders who map a year of bills to the EIA price on each bill date are the ones who catch the drift [1][2].

The catch

A table that heavily lags the market leaves a carrier losing money on a route [2]. A carrier bleeding cash on your freight becomes a huge risk at the next volume peak, not a smart saving.

The thing to debate is the formula itself, not whether fuel gets priced at all.

My read is that the peg and the MPG move the final bill far more than the headline rate does. Yet plenty of shippers have never seen either figure in their deals.

At a glance

  • The Big Shift: The fuel fee on a freight bill comes from a carrier’s own math — the peg, the MPG guess and the rate table — rather than a set diesel price [2][3][4].
  • Why It Matters: The same diesel index yields vastly different fees across carriers. This makes the peg and the MPG guess matter more at renewal than the base rate [2][3].
  • What I’d Watch: How closely shippers check the math behind the bill.
  • The peg: The base diesel price a carrier drops before pricing fuel. A lower peg guarantees a higher fee at every price [3].
  • The MPG guess: The fuel economy written into the formula. A low figure makes the fee rise much faster than the real fuel cost [3].
  • The banding: The diesel ranges a carrier maps to set fee steps. The edges dictate where a tiny price move triggers a massive jump [4].
  • The Catch: Fuel is a real running cost. A table that under-prices it forces a carrier to lose money on a route — creating a risk rather than a true saving [2].

Related reading

Sources

[1] Energy Information Administration, “Gasoline and Diesel Fuel Update” — https://www.eia.gov/petroleum/gasdiesel/ [2] Dashdoc, “What is a Fuel Surcharge in Trucking? Complete Guide” — https://www.dashdoc.com/en-us/blog/fuel-surcharge-trucking-complete-guide [3] The Freight Guru, “Fuel Surcharges in Trucking Explained” — https://thefreightguru.io/fuel-surcharge-trucking-explained [4] Freightera, “How Diesel Prices Affect Your Freight Rates” — https://www.freightera.com/freight-shipping-guide/how-diesel-prices-affect-your-freight-rates