Diesel finished last week at $5.652 a gallon on the national average — up 19.8 cents in seven days, and 40 cents since August 10. The number that should stop you is the year-over-year one: nearly two dollars a gallon more than the same week last year. At six miles to the gallon, that is 32 cents a mile of brand-new cost on a truck doing exactly what it did in 2025.
Absorbing that is what a fuel surcharge is for. It rarely absorbs all of it, and the shortfall isn't anybody being sneaky — it's arithmetic, sitting in a table most people never ask to see.
A surcharge is a reimbursement, not a raise
The line exists so a rate doesn't have to be renegotiated every time the pump moves. Linehaul is what you're paid to move the freight. The surcharge is what's supposed to make you whole on fuel above some baseline. Once you hold those two apart, "three-ten a mile" stops being one number and starts being two — and only one of them is your pay.
The standard math is a single line: (this week's diesel price − a base price) ÷ an assumed mpg = surcharge per mile. Run last week's average against a $1.25 base at 6 mpg and it comes out around 73 cents a mile.
Every input in that line is somebody's assumption. The price comes from the EIA's on-highway diesel average, published fresh every week. The base is whatever the table says it is — there is no regulated figure, and whatever sits in that blank is assumed to already be buried inside your linehaul. And the mpg describes a truck that may not be yours.
Leak one: the table's truck, not your truck
Six miles per gallon is the assumption you'll meet most often. Say your truck really turns 5.5 — heavy freight, hills, a winter, an older aero package. The surcharge still pays you as though it turned 6.
Run it at last week's price. At 6 mpg, $5.652 diesel costs 94.2 cents a mile. At 5.5, that same fuel costs $1.028 a mile. The table covers the first number. You buy the second.
Nobody sends you a bill for that. It just never arrives.
Leak two: a national index, a regional pump
Most tables peg to the national average. Last week that was $5.652 — while the Gulf Coast averaged $5.481 and the West Coast averaged $6.407. That's a spread of about 93 cents a gallon between the cheap end of the country and the expensive one, and a national-index surcharge pays a California mile exactly what it pays a Texas mile.
Buy that fuel out west at 6 mpg and you're roughly 13 cents a mile short of what the load reimbursed. Buy it on the Gulf Coast and the same surcharge hands you more than the fuel actually cost. That isn't a loophole — it's the whole reason fuel routing is a skill and not a preference. The diesel playbook is the other half of this piece.
Leak three: the number that hides both
Spot rates posted on a load board are all-in. DAT reports them that way — linehaul and fuel bundled into one figure — while contract rates usually carry the surcharge broken out beside them.
So when the pump climbs 40 cents in two weeks and the board still shows $3.10 a mile, the linehaul underneath it just got cut, and nobody had to say a word to you. Your rate didn't fall. Your pay did. The first thing to do with an all-in number is split it — because comparing this week's all-in against last month's all-in is comparing two different questions and calling it one.
Four things worth doing
- Know your real mpg — loaded, in the season you're actually in. Not the sticker, not last spring's.
- Ask for the table. The base price and the assumed mpg are line items, they vary by contract, and almost nobody asks to see them.
- Back the fuel out of every all-in number before you compare two loads, or two months.
- Reprice weekly. The index moves every week. A rate floor built on last month's diesel is already wrong.
None of this makes fuel cheaper. It makes it visible, which is the only version you can price against. This week's number and all five regions are on the diesel prices page, refreshed every week off the EIA's own number. Put your real mpg and your real cost per gallon into the cost calculator — and the surcharge stops being a line you hope covers it, and starts being a number you can check.