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FAIR VALUE OF FINANCIAL INSTRUMENTS - USO's Securities Fair Value Hierarchy (Details) - USD ($) | Mar. 31, 2021 | Dec. 31, 2020
--- | --- | ---
United States [Member] |  |
FAIR VALUE OF FINANCIAL INSTRUMENTS |  |
Securities, fair value | $ (26,921) | $ (21,964)
Short-Term Investments [Member] |  |
FAIR VALUE OF FINANCIAL INSTRUMENTS |  |
Securities, fair value | 7,000,000 | 1,000,000
Fair Value, Inputs, Level 1 [Member] | United States [Member] |  |
FAIR VALUE OF FINANCIAL INSTRUMENTS |  |
Securities, fair value | (26,921) | (21,964)
Fair Value, Inputs, Level 1 [Member] | Short-Term Investments [Member] |  |
FAIR VALUE OF FINANCIAL INSTRUMENTS |  |
Securities, fair value | $ 7,000,000 | $ 1,000,000

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- Definition Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
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