"When a product doesn't reach its destination for a period of time, it often loses the value that it originally had." said The Salvage Groups owner Tom Enders.

When that happens, customers sometimes refuse to accept the goods or abandon them. In either case, Mr Enders declared shipping lines can contact a company to recover as much value from it as they can.

Stranded shipments lose worth in countless ways. For example, food and other perishables can spoil; seasonal merchandise might not reach a wholesaler's hands before the weather turns; machinery intended for a construction project might arrive too late for the job, etc.

Said Crown Salvage managing director Paul Vidler: "You leave a container on the quay for six months, you don't want to know what the bill is, it's frightening."

Shipping rates have doubled since April, and containers are in short supply around the world.

Said Mr Enders: "No one in the supply chain makes money when stuff is sitting idle. They make money when they're moving stuff."

Houston-based Salvex, one of the main players in the US, boasts that it has US$5.2 billion worth of goods for sale on its online marketplace, though not all are maritime container salvage.

The size of the buyers' profits hinges on how quickly they can get rid of what they acquire.

When the goods are worthless or dangerous they take a cut of the disposal fee; when the goods have value they make a profit on the resale, meaning every case is different.

US cargo salvage buyers expect the market on their side to catch up.