In a voluminous new report reflecting two years of research, an influential Senate panel accuses Goldman Sachs of manipulating aluminum storage rules in order to line its own pockets, even as manufacturers and customers suffered.

Since 2010, when it acquired the metal storage company Metro International Trade Services, Goldman has engaged in a slew of manipulative "merry-go-round" trades in which aluminum slabs are moved from one warehouse facility to another, says the 396-page report by the Senate Permanent Subcommittee on Investigations, resulting in record U.S. fees for storing and shipping aluminum and, as a result, higher overall costs for aluminum-product manufacturers and consumers.

"These merry-go-round transactions lengthened the metal load out queue to exit the Metro warehouse system [and] blocked the exits for other metal owners seeking to leave the system," states the report, unveiled at 5 p.m. on Wednesday in advance of a two-day hearing set to be held on the subject in Washington, D.C.

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Those actions, combined with "extensive aluminum trading" that Goldman engaged in in the aluminum market during that period, the report adds, have "given rise to serious questions about the integrity of the aluminum market."

Early in the week of the report's release, the Senate hearings were already promising to be contentious. In its own 31-page position paper, prepared in advance of the release of the subcommittee's report, Goldman officials defended their actions with Metro and other commodity businesses. "The queues were the result of metal owners' independent, financially-motivated decisions to remove metal that had been placed in Metro's warehouses," the report stated. "Like any other landlord, Metro was merely competing for tenants."

Goldman enhanced its own profits in the physical storage and trading of aluminum, the Senate panel report argues, by purchasing Metro, a longtime warehousing business that stores aluminum, copper, zinc, and other base metals around the U.S.; stacking Metro's board exclusively with Goldman executives; and then striking backroom deals with aluminum owners like the international trading firm Glencore and the London hedge fund Red Kite.

Those deals allowed Metro to remove each client's aluminum from one Metro warehouse and move it shortly thereafter into another—tying up its ground transportation systems and creating substantial delays for other clients wanting to ship metal out of storage.