The producer price index for No. 2 diesel fuel stood 77.8% higher in August 2026 than a year earlier, after a single-month jump of 24.1% — a move that turns dormant fuel-adjustment clauses in freight contracts into active invoice drivers for shippers preparing 2027 bids.

The Bureau of Labor Statistics figure is a producer-price measure, not a proxy for any carrier's pump cost or a specific buyer's freight bill. Its significance for shippers is mechanical: large fuel swings activate adjustments in contracts that tie charges to an agreed index, converting a negotiated price into a moving one.

Rail provides the clearest evidence of how material those clauses have become. Norfolk Southern's 10-Q reports that contracts covering approximately 95% of its revenue include negotiated fuel surcharges. Fuel-surcharge revenue reached $415 million in the second quarter of 2026, more than double the $203 million recorded a year earlier. The figures describe one railroad's contract base, but they show a surcharge can be financially significant long after the underlying service contract was signed.

Ocean freight carries the same structural exposure. Bunker and emissions surcharges sit outside a carrier's headline rate entirely, meaning the rate a shipper negotiates and the invoice it eventually receives can diverge the moment energy inputs move.

The lag problem

Timing can matter as much as the index itself. Covenant Logistics' filings state that most of its fuel surcharges use the Department of Energy's average price for the week before shipment, so the carrier typically bills customers in the current week against the prior week's index. The lag cuts both ways. During a sharp increase, the carrier recovers less than its current fuel cost; when prices fall, the reverse occurs.

For the buyer, a weekly adjustment means an approved transportation rate can still produce a different invoice a week later. It is the same disconnect between a signed price and what a supplier can deliver at that price that surfaces across fixed-price agreements once energy, freight and material costs move independently of the contract term.

Tariff pass-throughs now run in one direction

Tariff clauses add a second variable, and one public filing illustrates both sides of the exposure. LCI Industries' 2026 filings describe ongoing tariff-related cost pressure passed through to customers under index pricing — and, separately, a liability of roughly $88.8 million to pass IEEPA tariff refunds back to certain customers.

That reciprocity question is the useful contract test for shippers. If a supplier can raise a price when a tariff adds cost, does the buyer receive a corresponding adjustment when the tariff is reduced, removed, refunded or found inapplicable? The answer depends entirely on the agreement, product and duty paid. Buyers in energy contracts are already hitting the identical problem, where broad pass-through language accepted as boilerplate is generating invoices they never modeled.

What a review should cover

Before signing 2027 volume or price commitments, buyers should trace each adjustment from trigger to invoice. That means identifying the named fuel index, its publication date, the base price at which the surcharge begins, the update frequency, and whether a floor or cap applies. For tariffs, establish which product and import transaction qualifies, what proof of cost the supplier must provide, and when reductions or refunds flow back. Shippers should also check whether a supplier can stack overlapping fuel, freight, material and tariff adjustments on the same cost.

Leverage will differ by market. A buyer with several qualified carriers may push for tighter triggers, audit rights or a shorter adjustment period. A supplier facing volatile inputs may demand a pass-through in exchange for a lower base bid or a firm capacity commitment. Neither position resolves the core issue unless both parties agree on how the clause works when costs rise — and when they fall.

The evidence supports a contract review, not a claim that surcharge terms are universal. Shippers should start where transportation or imported inputs form a substantial share of cost, compare adjustment language across bids, and model price paths before awarding business. With diesel up 77.8% year on year and tariff litigation still generating refund liabilities, 2027 outcomes will hinge less on the lowest opening quote than on which supplier offers the most predictable final price.