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Fair Value Measurements (Tables)
9 Months Ended
Sep. 30, 2012
Assets And Liabilities Measured At Fair Value
     September 30,
2012
     December 31,
2011
 

United States Treasury Obligations (Level 1)

   $ 1,629,797,437       $ 1,959,875,160   

Commodity Futures Contracts (Level 1)

   $ 175,469,983       $ (135,420,844