"... the ability of a few traders to hold huge swaths of the world's stockpiles is coming under scrutiny.
The latest example is in the copper market, where a single trader has reported it owns 80% to 90% of the copper sitting in London Metal Exchange warehouses, equal to about half of the world's exchange-registered copper stockpile and worth about $3 billion.
Single traders also own large holdings of other metals. One trader holds as much as 90% of the exchange's aluminum stocks. In the nickel, zinc and aluminum alloy markets, single traders own between 50% to 80% of those metals and one firm has 40% to 50% of the LME's tin stockpiles.
While commodities exchanges scrutinize all holdings to ensure a single player isn't trying to corner the market, and many of the positions are owned by big firms on behalf of clients, the large holdings do result in a concentration of ownership that could skew prices."
I had no idea such concentrations were regularly common. And before we all panic, remember that a firm may own if for many many clients.