Container freight rates can multiply and then collapse within a single year, while the volume of goods being moved changes only modestly. The mismatch is built into how shipping capacity is created.
Capacity cannot respond quickly
A container ship is ordered years before it sails, because shipyard slots are booked well ahead and construction itself takes a long time. Capacity arriving this year reflects decisions taken in a very different market.
Removing capacity is equally slow. A ship represents decades of remaining life, and scrapping it early means writing off an asset that would otherwise earn for years, so owners resist until losses are severe.
The supply curve is therefore close to vertical in the short run. When demand rises, no additional ships appear, and the entire adjustment has to happen through price rather than through volume.
Small demand shifts produce large price moves
When a fleet is running near full, an extra few percent of cargo has nowhere to go. Shippers who must move goods bid against each other, and rates rise until enough of them withdraw.
The same mechanism works in reverse. Once utilisation slips below the point where every slot is contested, operators cut price to fill space, because a sailing departs whether the slot is sold or not.
This asymmetry between fixed capacity and variable demand explains why freight indices are among the most volatile prices in international trade, far more so than the goods being carried.
Disruption removes capacity without removing ships
Port congestion, canal restrictions and rerouting around a longer path all absorb vessel time. The same fleet completes fewer round trips per year, which reduces effective capacity even though no ship has left the market.
Containers themselves become scarce in the same way. Boxes sitting in a congested port are not available for loading elsewhere, so equipment shortages appear in regions far from the original disruption.
Because these effects compound, a delay measured in days at one chokepoint can tighten global capacity for months and move rates far more than the physical obstruction alone would suggest.
Contract and spot markets diverge
Large shippers negotiate annual contracts at fixed rates, while the remainder buy space on the spot market. In a tight market the spot rate can rise far above the contract rate.
Carriers then face a commercial choice about which cargo to load, and contract holders sometimes find their allocations squeezed even where volumes were agreed in advance.
When the market loosens, the positions reverse and contract rates sit above spot, so shippers seek to renegotiate. The cycle rewards whichever side is less desperate at the moment of the discussion.
The cycle is self-reinforcing
High rates fund large newbuilding orders, since owners commit capital when returns look strongest. Those ships arrive years later, frequently into a market that has already softened.
The resulting overcapacity depresses rates for an extended period, ordering stops, and the fleet slowly tightens again as older vessels leave service.
Shipping has run this pattern for as long as records exist, which is why experienced operators treat exceptional rates as temporary rather than as a new baseline.