EXHIBIT 99 CERTIFICATION PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002 (SUBSECTIONS (A) AND (B) OF SECTION 1350, CHAPTER 63 OF TITLE 18, UNITED STATES CODE) Pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 (subsections (a) and (b) of Section 1350, Chapter 63 of Title 18, United States Code), each of the undersigned officers of USG Corporation, a Delaware corporation (the "Company"), does hereby certify, to the best of his knowledge, that: The Annual Report on Form 10-K for the year ended December 31, 2002 (the "Form 10-K") of the Company fully complies with the requirements of section 13(a) or 15(d) of the Securities Exchange Act of 1934 and information contained in the Form 10-K fairly presents, in all material respects, the financial condition and results of operations of the Company. February 27, 2003 /s/ William C. Foote ------------------------------------ William C. Foote Chairman, Chief Executive Officer and President February 27, 2003 /s/ Richard H. Fleming ------------------------------------ Richard H. Fleming Executive Vice President and Chief Financial Officer 99