How do I build a fuel surcharge for Mexico freight?

What a U.S. fuel surcharge is written against

Most fuel surcharges in U.S. trucking are written against one number: the On-Highway Diesel Fuel Price published weekly by the U.S. Energy Information Administration. Prices are collected Monday and published Tuesday morning, with the occasional holiday shift. Both sides of a contract can open the same page and agree on what it says.

Worth being precise about what that does and does not settle. A shared reference makes the arithmetic agreeable. It does not settle the formula, the timing, or what happens in a dispute. The EIA is explicit that surcharge methods are left to private negotiation.

Mexico publishes diesel prices. None of them plays that role.

It would be wrong to say Mexico has no published diesel price. It does, from more than one source:

• The CNE. The station-price tool gives retail prices per station, searchable by state and municipality, updated daily. Its open-data catalog also publishes daily national averages and monthly state averages.
• Profeco. Publishes national average fuel prices built from station reports, and describes them as reference figures subject to change.
• INEGI. Its price indices include fuel, but they measure change rather than a per-litre rate, so converting one into pesos per litre needs assumptions both parties would have to agree.

So the honest problem is not absence. It is that none of these has become the thing a Mexican freight contract is routinely written against, the way the EIA series has in the United States. Before you pick one, settle the things that actually decide whether a clause holds: the methodology behind the number, how long after the fact it publishes, whether there is an archive you can point back to, and whether your counterparty will accept it. Those questions are open in a way they simply are not in the United States.

Why the Mexican pump price does not track world diesel

This is the part that breaks a copied formula.

Mexico charges a fixed excise on diesel, the IEPS, set as a quota per litre and adjusted annually. Separately, the finance ministry publishes a weekly stimulus percentage in the Diario Oficial de la Federación that waives some portion of it. The waiver is not always partial and not always the same: it has ranged from nothing to the entire quota.

A dated illustration rather than current guidance: for 2026 the diesel quota was set at 7.3634 pesos per litre, and in the week of 12 September 2026 the excise was waived in full, having been at roughly 91 per cent the week before. Both figures were accurate when written and neither is a current number. The quota changes each January and the stimulus changes weekly.

There has also been a voluntary arrangement between the federal government and fuel retailers to hold diesel near a target price. It is an agreement rather than a control, and it can change.

The consequence for a formula: the Mexican pump price is a market price with a variable tax offset sitting on top of it. A clause that assumes the pump tracks world diesel will misprice when the offset moves.

And one trap worth naming. If you index to an observed Mexican retail price, that price already contains whatever stimulus was applied that week. Applying the stimulus again as a separate adjustment counts it twice. Decide which one your clause uses, and say so.

What a defensible Mexico surcharge needs

There is no settled convention here, so what you write is a negotiation rather than a standard. Five things make it hold:

1. A named source with a stated cadence. Publisher, exact series, the day it publishes, the day your surcharge resets. Most disputes are about timing, not arithmetic.
2. A stated position on tax. Pre-tax or at-pump, and therefore whether the stimulus is already inside your reference number.
3. A stated unit conversion. Mexican diesel is priced in pesos per litre, U.S. diesel in dollars per U.S. gallon, and one U.S. gallon is exactly 3.785411784 litres. If your lane crosses the border, say which leg uses which.
4. A named exchange rate with its own timing. None of the fuel sources carry a currency conversion. Without naming the FX source and the observation date, you have moved the argument from fuel to currency.
5. Rules for the awkward cases. What happens on a decrease, whether there is a floor or cap, how you round, and what you do when an observation is missing or the source is discontinued.

How settled is any of this

Not very, and that is worth knowing before you assume there is a standard to copy. A few large carriers publish a bracket table for their own Mexico services, where a surcharge percentage steps up with a published fuel price. Those tables are set unilaterally by the carrier, they change without notice, and they cover that carrier's own services rather than truckload freight generally, so they are a shape to borrow rather than a benchmark to cite.

Trade coverage of the subject observes that the fuel surcharge concept has not taken hold in Mexican trucking the way it has in the United States. We looked for worked legal or consulting guidance on drafting a Mexico surcharge clause and did not find a public one, which is not the same as proving none exists.

Where rate data fits, and where it does not

A benchmark will not build your surcharge, and it cannot audit one.

Cargado's bands are what carriers bid to move the freight, to the truck, across a rolling twelve-week window refreshed weekly. That means two things. They sit below a rate you pay a broker or forwarder, which carries their margin and whatever services you bought. And they are a blended all-in number, so they cannot separate the fuel component from capacity, equipment, service level or timing. You cannot use them to check whether a fuel mechanism is calculating correctly.

What they are good for is the wider question: whether the lane is priced where the market is. Compare like for like, against your own baseline, and treat a gap as something to understand rather than something to correct.