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FAIR VALUE OF FINANCIAL INSTRUMENTS - Valuation of USO's securities (Details) - USD ($)
Sep. 30, 2025
Dec. 31, 2024
Short-Term Investments    
FAIR VALUE OF FINANCIAL INSTRUMENTS    
Securities fair value $ 675,000,000 $ 727,450,000
Exchange-Traded Futures Contracts | Swap | OTC Commodity Swap Contracts    
FAIR VALUE OF FINANCIAL INSTRUMENTS    
Securities fair value 91,039 (2,068)
Exchange-Traded Futures Contracts | United States Contracts    
FAIR VALUE OF FINANCIAL INSTRUMENTS    
Securities fair value (2,068,190) 28,431,020
Level 1 | Short-Term Investments    
FAIR VALUE OF FINANCIAL INSTRUMENTS    
Securities fair value 675,000,000 727,450,000
Level 1 | Exchange-Traded Futures Contracts | United States Contracts    
FAIR VALUE OF FINANCIAL INSTRUMENTS    
Securities fair value (2,068,190) 28,431,020
Level 2 | Exchange-Traded Futures Contracts | Swap | OTC Commodity Swap Contracts    
FAIR VALUE OF FINANCIAL INSTRUMENTS    
Securities fair value $ 91,039 $ (2,068)