US on-highway diesel averaged $5.652/gal in the EIA's survey for Aug 24, 2026. At the conventional $1.25 base and 6.0 MPG, that is a fuel surcharge of 73.37¢ per mile — about $366.83 on a 500-mile load. Adjust the peg, MPG and diesel price below to match your own contract.
The standard (diesel − base) ÷ MPG contract formula.
Formula: FSC per mile = (diesel price − base price) ÷ MPG. The surcharge floors at zero — if diesel falls below the base, contracts do not normally charge the shipper a negative surcharge.
Cents per mile across a range of diesel prices, at your peg and MPG.
Many contracts publish exactly this kind of stepped table rather than a live formula, fixing the surcharge for each band of diesel prices. The rows follow whatever base and MPG you set on the left.
| Region | Diesel $/gal | FSC ¢/mile at $1.25 & 6.0 MPG |
|---|---|---|
| East Coast | $5.498 | 70.80¢ |
| Midwest | $5.636 | 73.10¢ |
| Gulf Coast | $5.481 | 70.52¢ |
| Rocky Mountain | $5.537 | 71.45¢ |
| West Coast | $6.407 | 85.95¢ |
Regional pegs matter on lanes that run inside one market — see diesel prices by region for the full survey and diesel price history for the longer trend.
Fuel is the second-largest cost of running a truck after the driver, and it moves far faster than freight rates can be renegotiated. Without a surcharge, a carrier quoting a rate today is effectively taking a position on diesel for the length of the contract — and in a year like 2022, when diesel moved more than two dollars a gallon, that position can be larger than the entire margin on the freight.
Splitting the invoice fixes that. The base rate covers the driver, the tractor, insurance and overhead, and is negotiated on service. The surcharge covers fuel and is mechanical: both sides agree the formula once, then look up the same public EIA number each week. Because the reference is the government's own survey rather than either party's fuel bill, there is nothing to audit and little to argue about.
The negotiation moves instead to the two assumptions. A shipper wants a high MPG assumption and a high base price, since both shrink the surcharge; a carrier wants the reverse. Neither number has to match the truck's real fuel economy, and often it does not — which is why a carrier running newer, more efficient equipment than the contract assumes can earn a genuine margin on the surcharge itself.
A fuel surcharge is a separate line on a freight invoice that moves with the price of diesel, so neither carrier nor shipper is betting on fuel when they agree a rate. The base freight rate covers everything else; the surcharge floats. Almost every US contract pegs it to the EIA weekly on-highway diesel average, because it is published by the government, applies nationally, and cannot be influenced by either party.
The standard formula is (current diesel price − base price) ÷ truck MPG. If diesel is $4.25, the contract base is $1.25 and the truck averages 6 MPG, that is ($4.25 − $1.25) ÷ 6 = $0.50 per mile. Multiply by loaded miles for the surcharge on the load. Some contracts instead use a published table that steps the surcharge every few cents of diesel, but the underlying arithmetic is the same.
There is no legal standard — they are negotiated. A $1.20–$1.25 base is the long-standing convention, dating from when diesel actually cost that. MPG assumptions usually sit between 5.5 and 6.5 for a loaded class-8 tractor. Both numbers matter: a lower base or a lower MPG produces a larger surcharge, so they are exactly what gets argued over in contract talks.
The EIA publishes a national on-highway diesel average every Monday afternoon, plus regional averages for the PADD districts and California. National is the usual peg. Regional pegs are fairer on lanes that sit entirely inside an expensive market such as California, where the retail price runs well above the national number. This page seeds the national figure and lets you substitute any regional price.