* Filed herewith 141 31.1* Certification of CEO filed pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 31.2* Certification of CFO filed pursuant to Section 302 of the Sarbanes-Oxley Act of 2002 32.1* Certification of CEO furnished pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 32.2* Certification of CFO furnished pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 95.1* Mine Safety Disclosure 99.1* Reserve Audit Report of Netherland, Sewell & Associates, Inc., dated February 7, 2020 101.1* Interactive Data Files Pursuant to Rule 405 of Regulation S-T, formatted in Inline XBRL: (i) Consolidated Statements of Operations for the three years ended December 31, 2019, (ii) Consolidated Statements of Comprehensive Income for the three years ended December 31, 2019, (iii) Consolidated Balance Sheets as of December 31, 2019 and 2018, (iv) Consolidated Statements of Cash Flows for the three years ended December 31, 2019, (v) Consolidated Statements of Changes in Equity for the three years ended December 31, 2019 and (vi) Notes to Consolidated Financial Statements 104.1* The cover page from the Company's Annual Report on Form 10-K for the year ended December 31, 2019, formatted in Inline XBRL (included in Exhibit 101) Table of Contents Index to Financial Statements