If you read our previous piece on ocean freight surcharges, you already know that a fixed-rate contract is not actually fixed. The base rate may be locked, but fuel surcharges float, peak season surcharges stack, and emergency fees appear with little warning. The total cost of moving a container under an annual service contract can vary significantly from month to month even when the contracted rate never changes.
That gap between what shippers expect to pay and what they actually pay is the problem index-linked contracts are designed to solve. This piece explains what they are, how they work mechanically, and when they make sense -- and when they do not.
The traditional annual service contract works like this: a shipper and carrier negotiate a rate per container on a given lane, lock it in for 12 months, and agree on a minimum volume commitment. The shipper gets price certainty. The carrier gets volume predictability. In theory, both sides benefit.
In practice, the model breaks down in volatile markets. When spot rates rise sharply above the contracted rate, carriers have little incentive to honor space commitments -- rolling cargo in favor of higher-paying spot shippers becomes financially rational. When spot rates fall well below contracted rates, shippers have little incentive to honor volume commitments -- they route freight to the spot market and leave the carrier with empty space.
The result is a contract that neither side fully honors when the market moves against them. The renegotiation cycles, rolled cargo, and strained carrier relationships that follow are not anomalies. They are the predictable behavior that fixed-rate contracts produce when market rates diverge far enough from contracted rates.
This dynamic played out repeatedly between 2020 and 2024, as spot rates swung from historic highs during COVID-era congestion to sharp collapses in late 2022, then spiked again during the Red Sea crisis in 2024. Shippers who locked in contracts at peak rates found themselves overpaying by thousands of dollars per container when spot collapsed. Carriers who signed contracts at low rates found them uneconomical when spot surged. Both sides learned the same lesson: a fixed rate set at a single point in time is a bet on where the market will be for the next 12 months, and that bet is frequently wrong.
An index-linked contract is an ocean freight agreement where the rate is not fixed for the contract term. Instead, it is tied to a published freight index and adjusts automatically at defined intervals -- monthly or quarterly -- based on where that index moves.
The shipper and carrier still negotiate the core terms: the trade lane, the container type, the volume commitment, and the adjustment mechanism. What they do not do is agree on a single rate and hold it regardless of where the market goes. Instead, they agree on a formula: the rate will equal the index value, or the index value plus or minus a spread, reset on a defined schedule.
This structure keeps the contracted rate aligned with the market throughout the contract term. When freight rates rise, the contracted rate rises with them. When rates fall, the contracted rate falls too. Neither party is locked into a rate that has gone significantly out of alignment with market reality, which removes the primary incentive to roll cargo or abandon volume commitments.
The concept is not new to global trade. Commodity markets have used index-linked pricing for decades. Oil contracts are priced against Brent or WTI. Grain contracts reference the Chicago Board of Trade. LNG contracts link to Henry Hub. Ocean freight is applying the same logic to container shipping -- and doing so later than most commodity markets largely because reliable, transaction-based freight indices did not exist at the necessary level of granularity until recently.
Consider a shipper moving 40-foot containers from Shanghai to Los Angeles. They negotiate an index-linked contract with a carrier structured as follows:
The contracted rate will equal the relevant freight index value for the Shanghai to Los Angeles lane, reset monthly based on the index reading at the start of each month, with the shipper committing to a minimum of 50 containers per month.
In January, the index reads $2,800 per FEU. The shipper pays $2,800.
In February, market conditions tighten due to early peak season demand and the index moves to $3,200. The contracted rate adjusts automatically to $3,200. The shipper pays the higher rate, but so does everyone else in the market. The carrier has no incentive to roll their cargo in favor of spot shippers because the contracted rate is already at market.
In March, capacity loosens and the index drops to $2,400. The contracted rate adjusts to $2,400. The shipper benefits from the lower market rate without needing to renegotiate or threaten to move volume to spot. The carrier retains the committed volume because the contracted rate is competitive with what the spot market is offering anyway.
Neither party needed to pick up the phone to renegotiate. Neither party had an incentive to defect. The contract self-corrected because the rate was tethered to reality.
In practice, many index-linked contracts include a spread above or below the index to account for service level, equipment availability, or commercial relationship. A shipper might agree to pay index plus $200 per FEU in exchange for guaranteed space priority. The spread is negotiable. The mechanism is the same.
These are the three primary structures available in ocean freight contracting, and each one involves a different tradeoff between cost certainty and market alignment.
Fixed-rate contracts lock the base rate for the contract term. They offer budget predictability but embed rate risk: if the market moves significantly in either direction, one party is disadvantaged and behavioral incentives shift accordingly. Fixed-rate contracts also embed surcharge risk, as discussed in the previous piece -- the base rate is locked but floating surcharges are not.
Spot contracts reflect the current market rate at the time of booking, typically one to two weeks out. They offer maximum flexibility and allow shippers to capture falling rates immediately. They also expose shippers to full upside rate volatility, make budgeting difficult, and provide no guarantee of space during capacity-constrained periods.
Index-linked contracts sit between the two. The rate floats with the market but within a structured, agreed framework rather than the open spot market. Shippers give up the certainty of a fixed rate in exchange for market alignment and the behavioral benefits that alignment produces. They retain the commitment of a contract -- guaranteed space, agreed volume, defined service terms -- without the rate risk that fixed contracts carry.
No single structure is universally correct. The right choice depends on a shipper's volume profile, budget flexibility, lane characteristics, and risk tolerance. Many sophisticated shippers use all three in combination, allocating high-volume predictable lanes to index-linked contracts, stable secondary lanes to fixed-rate contracts, and irregular or low-volume lanes to spot.
Index-linked contracts were rare before 2023. When they were used at all, it was primarily to recalibrate multi-year contracts rather than as a standard procurement structure. The conditions that existed before 2020 -- relatively stable freight rates, predictable seasonality, functioning carrier commitments -- made fixed-rate contracts workable enough that most shippers never needed an alternative.
The volatility of 2020 through 2024 changed that calculus. As spot rates swung from $2,000 to $20,000 per FEU and back, the limitations of fixed-rate contracting became impossible to ignore. Shippers who had committed to rates that went out of alignment with the market by thousands of dollars per container understood the behavioral problem firsthand.
The growth since then has been rapid. The number of ocean freight contracts structured as index-linked has roughly doubled annually for two consecutive years. They now represent approximately 8 percent of contract volume on the major east-west trades, with two-thirds of the world's leading ocean carriers offering them as a standard option. What was a niche instrument used primarily by sophisticated BCOs is becoming a mainstream procurement choice.
Improved data quality has been a key enabler. Index-linked contracts require an index that market participants trust -- one that accurately reflects what shippers and carriers are actually paying, not what they are quoting or bidding. The development of transaction-based freight indices, built from actual shipped-on-board rates rather than survey or quoted-rate data, has given the market a reliable foundation to link contracts to.
Index-linked contracts are not universally better than fixed-rate contracts. They involve real tradeoffs that every shipper should understand before adopting them.
You give up cost certainty. A fixed-rate contract tells you exactly what you will pay per container for the next 12 months, which makes budgeting straightforward. An index-linked contract does not. If the index rises sharply -- as it did during the 2024 Red Sea crisis or the 2026 Hormuz disruption -- your contracted rate rises with it. The behavioral benefits of alignment cut both ways: you stay aligned with the market whether the market is favorable or not.
You take on index risk. The rate you pay is only as accurate as the index you are linked to. An index that does not closely track the specific lane, container type, and time period of your actual shipments can produce rates that diverge from your real market even while appearing to be market-linked. This is a meaningful risk and the primary reason index selection requires serious evaluation -- a topic we cover in the next piece in this series.
You add operational complexity. Fixed-rate contracts are administratively simple. The rate is the rate. Index-linked contracts require tracking index movements, understanding the reset mechanism, and reconciling invoices against index values each period. For shippers without the systems or bandwidth to manage that process, the operational overhead can offset the structural benefits.
You may face resistance from carriers. Not all carriers offer index-linked contracts on all lanes. Smaller carriers and NVOCCs may have limited familiarity with the structure or may be unwilling to accept index exposure without significant spread compensation. Availability varies by trade lane and carrier relationship.
It is the most instinctive objection to index-linked contracts, and it deserves a direct answer.
The assumption behind the objection is that a fixed-rate contract offers genuine cost certainty, and that agreeing to a floating rate means giving that certainty up. If rates rise, you pay more. Why would any shipper sign up for that?
The problem is that the certainty a fixed-rate contract appears to offer is largely an illusion -- and the previous piece in this series is the proof. When Iran blocked the Strait of Hormuz in early 2026, shippers under fixed-rate contracts did not pay their contracted rate. They paid their contracted rate plus emergency bunker surcharges, emergency freight increases, and war risk adjustments that carriers declared and applied unilaterally on top of the locked base rate. In some cases that added $3,000 or more per FEU to invoices that were supposed to be predictable.
That is the fundamental flaw in fixed-rate contracting that rarely gets stated plainly: the carrier controls the surcharge stack. The base rate is locked. Everything on top of it is not. And in a volatile market, carriers have both the mechanism and the incentive to recover their cost increases through surcharge declaration rather than base rate renegotiation. The fixed-rate contract gives the shipper the appearance of protection while leaving the most volatile cost components entirely in the carrier's hands.
An index-linked contract pegged to a well-constructed, transaction-based freight index works differently. The index reflects what shippers and carriers are actually paying in the market -- real transactions, shipped on board, cleared at actual market rates. When costs rise because fuel prices spike or capacity tightens, the index moves. The contracted rate moves with it. But what the index captures is the genuine market cost of that volatility -- not a carrier's surcharge declaration layered on top of a base rate that was never designed to absorb it.
The practical difference is significant. Under a fixed-rate contract during a market spike, the carrier declares surcharges. The shipper pays the base rate plus whatever the carrier determines the surcharges should be, with limited contractual recourse. Under an index-linked contract during the same market spike, the rate rises -- but it rises to where the market actually cleared, bounded by transaction data, not by what a carrier's tariff desk decided to charge. The shipper is paying market rate. They are not paying market rate plus a margin the carrier extracted through surcharge stacking.
When the market falls, the dynamic reverses. The index drops, the contracted rate drops, and the shipper captures the lower market rate automatically without needing to threaten a move to spot or renegotiate mid-contract. Under a fixed-rate contract in a falling market, that lower rate is inaccessible until the contract term expires or the carrier agrees to renegotiate -- which they have no incentive to do.
So the real comparison is not between cost certainty and cost uncertainty. It is between two different kinds of cost exposure. A fixed-rate contract exposes the shipper to unilateral surcharge declaration by the carrier on top of a locked base rate. An index-linked contract exposes the shipper to actual market movement, bounded by transaction data, in both directions. In a volatile market, the second form of exposure is the more honest and frequently the more manageable one.
The caveat -- and it is an important one -- is that this argument only holds if the index the contract is linked to accurately reflects the shipper's actual trade. An index that does not track the right geography, container type, or market segment can produce rate movements that diverge from the shipper's real cost environment, which reintroduces the very problem index-linking was supposed to solve. That is why index selection is not a detail. It is the decision the entire contract structure depends on, and it is what we cover in the next piece in this series.
Index-linked contracts are best suited to shippers with the following characteristics.
High-volume, recurring flows on major trade lanes. The behavioral benefits of alignment -- reduced rolling, better space reliability, fewer renegotiation cycles -- scale with volume. Shippers moving large numbers of containers on active east-west trade lanes will feel those benefits most directly. Low-volume or irregular shippers may not have enough negotiating leverage to structure a contract on favorable terms.
Budget flexibility or a finance function that can manage variable freight costs. If your organization requires a fixed freight budget for annual planning and cannot accommodate monthly rate variation, index-linked contracts create an internal problem even if they solve an external one. CFOs who already manage hedged commodity costs, fuel exposure, or currency risk tend to be more comfortable with the structure than those encountering variable-cost contracting for the first time.
Organizations willing to invest in index literacy. Understanding which index to link to, how the reset mechanism works, and how to audit invoices against index values requires genuine engagement from procurement and finance. Shippers who treat it as a plug-and-play substitute for fixed-rate contracts without developing that literacy tend to encounter problems downstream.
The structure of an index-linked contract is straightforward. The harder question -- and the one that determines whether the contract actually delivers what it promises -- is which index you link to.
Not all freight indices are constructed the same way. Some are built from quoted rates. Some from booked rates. Some from actual shipped-on-board transactions. Some cover broad trade aggregates. Others go down to subtrade or lane level. The difference between linking your Shanghai to Los Angeles contract to a pan-Asia index versus a lane-specific index can be worth hundreds of dollars per container in any given month -- not because the contract mechanism is broken, but because the index you chose does not accurately represent the rates on your specific trade.
Geography, data methodology, coverage, and update frequency all matter. Getting the index selection wrong does not eliminate rate risk -- it just substitutes one form of rate risk for another while adding a layer of complexity.
We cover the major freight indices available, how they are constructed, and how to evaluate which one is right for your contract in the next piece in this series.
Index-linked contracts are gaining adoption because they solve a real structural problem: fixed-rate ocean freight contracts create misaligned incentives when markets move, and markets in container shipping move more than they used to.
The tradeoffs are real. You give up the appearance of cost certainty in exchange for exposure to actual market movement, bounded by transaction data rather than unilateral carrier surcharge decisions. Whether that tradeoff makes sense depends on your volume profile, your organization's tolerance for variable costs, and your ability to select and monitor the right index.
NYSHEX builds contract management tools and freight indices specifically for this environment. If you are evaluating whether index-linked contracts make sense for your procurement strategy, NYSHEX offers a free contract simulator that models how index-linked structures would have performed on your lanes historically.
The next piece in this series covers the freight indices themselves -- what they measure, how they are built, and why selecting the right one is the decision that determines whether an index-linked contract works as intended.