As commodity prices soar to new records, 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%-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.

The report coincided with copper prices reaching record highs Tuesday. Commodities prices rallied along with stocks. The Dow Jones Industrial Average gained 55.03 points, or 0.5%, to 11533.16, its highest level since August 2008. Crude oil jumped to its highest level in more than two years and topped $90 a barrel in late electronic trading in New York. Corn and soybeans rose amid worries about hot weather in Argentina.

Copper soared to a new record of $4.2705 per pound Tuesday in New York and is up more than 28% this year. The LME's three-month copper contract closed at $9,353.50 a metric ton, up 1.6% on the day, a new record.