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UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON , D.C. 20549 FORM 10 - K 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 TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-36108 ONE Gas , Inc. ( Exact name of registrant as specified in its charter ) 46-3561936 Oklahoma ( State or other jurisdiction of incorporation or organization ) 15 East Fifth Street Tulsa , OK ( Address of principal executive offices ) Title of each class Common Stock , par value $ 0.01 per share ( I.R.S. Employer Identification No. ) Registrant's telephone number , including area code ( 918 ) 947-7000 Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol OGS 74103 ( Zip Code ) Name of exchange on which registered New York Stock Exchange Securities registered pursuant to Section 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 No 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 No 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 > No 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 > No 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 . ( Check one ) Large accelerated filer Accelerated filer Non - accelerated filer Smaller reporting company Emerging growth company 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 . On February 22 , 2021 , we had 53,243,986 shares of common stock outstanding . 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 . Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Act ) . Yes No The aggregate market value of the equity securities held by nonaffiliates based on the closing trade price of the registrant on June 30 , 2020 , was $ 3.9 billion . DOCUMENTS INCORPORATED BY REFERENCE : Portions of the definitive proxy statement to be delivered to shareholders in connection with the Annual Meeting of Shareholders to be held May 27 , 2021 , are incorporated by reference in Part III .