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Table of Contents ( Mark One ) ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 OR UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - K TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from Commission File Number 1-16417 Delaware ( State or other jurisdiction of incorporation or organization ) Securities registered pursuant to Section 12 ( b ) of the Act : Title of each class Large accelerated filer Non - accelerated filer NuStar NUSTAR ENERGY L.P. ( Exact name of registrant as specified in its charter ) р to 19003 IH - 10 West San Antonio , Texas 78257 ( Address of principal executive offices ) ( Zip Code ) Registrant's telephone number , including area code ( 210 ) 918-2000 NS NSprA NSprB NSprc ( I.R.S. Employer Identification No. ) Trading Symbol ( s ) 74-2956831 Common units Series A Fixed - to - Floating Rate Cumulative Redeemable Perpetual Preferred Units Series B Fixed - to - Floating Rate Cumulative Redeemable Perpetual Preferred Units Series C Fixed - to - Floating Rate Cumulative Redeemable Perpetual Preferred Units Securities registered pursuant to 12 ( g ) of the Act : None . Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes p No o Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes o No þ Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes þ No o Name of each exchange on which registered New York Stock Exchange New York Stock Exchange New York Stock Exchange New York Stock Exchange Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( §232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes þ No o Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company , or an emerging growth company . See the definitions of " large accelerated filer , " " accelerated filer , " " smaller reporting company , " and " emerging growth company " in Rule 12b - 2 of the Exchange Act : Accelerated filer Smaller reporting company Emerging growth company If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . O 00 Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Exchange Act ) . Yes No þ The aggregate market value of the common units held by non - affiliates was approximately $ 1.4 billion based on the last sales price quoted as of June 30 , 2020 , the last business day of the registrant's most recently completed second quarter . The number of common units outstanding as of January 31 , 2021 was 109,468,140 . DOCUMENTS INCORPORATED BY REFERENCE : Portions of the Proxy Statement for the registrant's 2021 annual meeting of unitholders , expected to be filed within 120 days after the end of the fiscal by this Form 10 - K , are incorporated by reference into Part III to the extent described therein . year covered