EXHIBIT 99.1

                            CERTIFICATION PURSUANT TO
                             18 U.S.C. SECTION 1350,
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Annual Report of the Arch Coal, Inc. Employee Thrift Plan
(the "Plan") on Form 11-K for the year ending December 31, 2002 as filed with
the Securities and Exchange Commission on the date hereof (the "Report"), the
undersigned, Steven F. Leer, Chief Executive Officer of Arch Coal, Inc.,
certifies, pursuant to 18 U.S.C. ss. 1350, as adopted pursuant to ss. 906 of the
Sarbanes-Oxley Act of 2002, that:

          (1) The Report fully complies with the requirements of section 13(a)
or 15(d) of the Securities Exchange Act of 1934; and

          (2) The information contained in the Report fairly presents, in all
material respects, the financial condition and results of operations of the
Plan.


                                    /s/ Steven F. Leer
                                    ------------------------------------
                                    Steven F. Leer
                                    President and Chief Executive Officer
                                    June 20, 2003


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