On-highway diesel averaged $6.285 a gallon for the week ending September 14, 2026 — a record in the EIA series, up 31.8 cents in a single week and $2.55 above the same week a year earlier. That is not a rounding error on your fuel line. On a truck turning 120,000 miles a year at 6 MPG, a $2.55 swing is roughly $51,000 of fuel per truck per year.
Most carriers have a fuel surcharge and assume it handles this. It partly does. The part it does not handle is where the money goes.
The formula, and the two numbers you negotiated
Nearly every US fuel surcharge in freight works out the same way:
(diesel price − peg price) ÷ MPG = surcharge per mile
The diesel price is almost always the EIA weekly national on-highway average. That part is not up for argument — it is a government figure neither side can push around, which is exactly why it became the standard.
The other two numbers are pure negotiation, and they are where the money actually sits.
Run it at this week's number with a conventional $1.25 peg and a 6.0 MPG divisor:
($6.285 − $1.25) ÷ 6.0 = 83.9¢ per mile, or about $419 on a 500-mile load.
Now change one input. Same diesel price, same peg, but the contract says 7.0 MPG because someone agreed to it in a softer market:
($6.285 − $1.25) ÷ 7.0 = 71.9¢ per mile — $60 less on that same load.
Nothing about your trucks changed. One divisor did.
The MPG divisor is the quiet one
A shipper wants a high MPG assumption and a high peg, because both shrink what they pay. You want the opposite. Fine — that is a negotiation, and both sides know it.
What is not fine is agreeing to an MPG you do not actually get. If your fleet averages 6.2 and the contract divides by 7.0, you under-recover on every single mile for the life of the agreement, and it never shows up as a line item anyone argues about. It shows up as margin that is mysteriously thinner than the rate sheet implied.
So the first thing to do this week is not renegotiate anything. It is to find out what your trucks actually return, by lane and by truck, from fuel purchases and odometer data rather than from what the spec sheet claimed. If you do not know that number, you cannot tell whether your surcharge is working.
The lag is real and it only hurts in one direction
The EIA figure is published weekly, and most surcharges reference the most recent published week. So when diesel jumped 31.8 cents in a week, carriers on a weekly reset spent that week buying fuel at the new price and billing against the old one. At 6 MPG, a 31.8-cent gap is about 5.3 cents a mile you ate.
That reverses when prices fall — you bill the old higher number while buying cheaper. Over a flat year it roughly washes out. In a sustained climb it does not, and this has not been a flat year.
Monthly or quarterly resets make the same effect bigger in both directions. If you are on a quarterly reset in a rising market, you are not slightly behind, you are a quarter behind. That is worth knowing before the next reset rather than after.
Check whether it pays on loaded miles or all miles
This one is simple and it is skipped constantly. Plenty of surcharge agreements pay per loaded mile. Your trucks burn diesel on empty miles too.
If you run 12% deadhead and the surcharge pays loaded-only, your effective recovery per mile driven is about 12% below the headline rate. At 83.9¢ that is roughly 10¢ a mile of real fuel cost with nothing attached to it.
That does not automatically mean you demand all-miles surcharge — it means you price deadhead into the linehaul when you cannot. Either is defensible. Not noticing which one you agreed to is not.
What to do this week
- Pull your real MPG. Fleet-wide, then by lane. Compare it to every MPG divisor you have signed.
- List your pegs. Older contracts carry pegs written when diesel was under $2.00. Some of those are generous to you now, some are not — but you should know which is which rather than discovering it at settlement.
- Check the reset cadence and the miles basis on your top five customers. Weekly or monthly, loaded or all miles.
- Recompute cost per mile with fuel at today's number, not last quarter's. A rate you accepted in June at $3.80 diesel is a different rate today. See what cost per mile actually includes if your number has not been rebuilt in a while.
None of that is a negotiation yet. It is the homework you need before one, and it is the difference between asking a customer for a peg change and telling them exactly what the current terms cost you per mile.
Where the software fits
The reason most carriers cannot answer "what is our real MPG on this lane" in under a minute is that fuel purchases live in a card portal, miles live in the dispatch system, and nobody joins them. That join is the whole job.
In TFS Fleet, fuel transactions and trip miles land against the same unit and the same load, so actual MPG and actual cost per mile are a report rather than a spreadsheet exercise. See Fuel & IFTA and Analytics.
The short version
Diesel at a record does not automatically break you — an honest surcharge is designed for exactly this. What breaks you is a surcharge built on an MPG you do not achieve, a reset slower than the market is moving, or a miles basis that ignores the empty miles you still pay for. Those were all decided in a contract, on a quiet day, and they are costing you today.
Check the live EIA number weekly while the market is doing this. Do not run your pricing off a figure you read in an article, including this one.