Simply storing all that metal generates tens of millions of dollars in rental revenues for Goldman every year.

There's just one problem: much less aluminum is leaving the depots than arriving, creating a supply pinch for manufacturers of everything from soft drink cans to aircraft.

The resulting spike in prices has sparked a clash between companies forced to pay more for their aluminum and wait months for it to be delivered, Goldman, which is keen to keep its cash machines humming and the London Metal Exchange (LME), the world's benchmark industrial metals market, which critics accuse of lax oversight.

Analysts question why London's metals market allows big financial players like Goldman to own the warehouses which store huge quantities of metal even as they trade the commodity. Robin Bhar, a veteran metals analyst at Credit Agricole in London says the conflict of interest is so acute he wants U.S. and European anti-trust regulators to weigh in.

"I think it makes a mockery of the market. It's a shame," Bhar said. "This is an anti-competitive situation. It puts (some) companies at an advantage, and clearly the rest of the market at a disadvantage. It's a real, genuine concern. And I think the regulators have to look at it."

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