EXHIBIT 99.4 THIRD SUPPLEMENTAL INDENTURE This Third Supplemental Indenture, dated as of December 31, 2005 (this "Supplemental Indenture"), among Ispat Inland ULC, a Nova Scotia unlimited liability company (the "Issuer"), the Guarantors, Mittal Steel USA ISG Inc. ("ISG") and LaSalle Bank National Association, as Trustee under the Indenture referred to below. WITNESSETH: WHEREAS, the Issuer, the Guarantors and the Trustee have heretofore executed and delivered an Indenture, dated as of March 25, 2004 (as heretofore amended, supplemented, waived or otherwise modified, the "Indenture"), providing for the issuance of Senior Secured Floating Rate Notes due 2010 and 9 3/4% Senior Secured Notes due 2014 of the Issuer (together, the "Notes"); WHEREAS, Ispat Inland Inc. ("Inland"), a Guarantor under the Indenture, will be merging with and into ISG, with ISG as the Successor Company; WHEREAS, Section 5.01(a) of the Indenture requires that upon a merger of Inland with or into another Person, the Successor Company shall execute and deliver a supplemental indenture pursuant to which such Successor Company will expressly assume all of the obligations of Inland under the Mortgage, the First Mortgage Bonds, Inland's Note Guarantee and the Indenture; WHEREAS, pursuant to Section 8.01 of the Indenture, the Issuer, the Guarantors and the Trustee are authorized to execute and deliver this Supplemental Indenture to amend or supplement the Indenture, without the consent of any Holder; WHEREAS, this Supplemental Indenture has been duly authorized by all necessary corporate action on the part of each of the Issuer, the Guarantors and the Trustee; NOW, THEREFORE, in consideration of the foregoing and for other good and valuable consideration, the receipt of which is hereby acknowledged, the Issuer, the Guarantors and the Trustee mutually covenant and agree for the equal and ratable benefit of the Holders of the Notes as follows: ARTICLE I DEFINITIONS SECTION 1.1 Defined Terms. As used in this Supplemental Indenture, terms defined in the Indenture or in the preamble or recital hereto are used herein as therein defined. The words "herein," "hereof" and hereby" and other words of similar import used in this Supplemental Indenture refer to this Supplemental Indenture as a whole and not to any particular section hereof. 1 ARTICLE II ASSUMPTION BY ISG SECTION 2.1 Agreement to be Bound as Guarantor. ISG hereby becomes a party to the Indenture as the Successor Company of Inland, as Guarantor of the Notes, and as such succeeds to, and is substituted for, and may exercise every right and power of, Inland under the Indenture and shall be subject to all of the obligations and agreements of Inland under the Indenture. ISG agrees to be bound by all of the provisions of the Indenture, the Mortgage, the First Mortgage Bonds and Inland's Note Guarantee applicable to Inland, and expressly assumes and agrees to perform all of the obligations and agreements of Inland under the Indenture, the Mortgage, the First Mortgage Bonds and Inland's Note Guarantee. SECTION 2.2 Trustee's Acceptance. The Trustee hereby agrees to accept this Supplemental Indenture and agrees, from and after the effective time of this Supplemental Indenture, to perform the same under the terms and conditions set forth in the Indenture. ARTICLE III MISCELLANEOUS SECTION 3.1 Notices. All notices and other communications to the Issuer or any Guarantor shall be given in the manner provided in the Indenture to the Issuer or such Guarantor at the address set forth below: Mittal Steel USA Inc. 4020 Kin Ross Lakes Parkway Richfield, OH 44286 Attention: General Counsel Fax: (330) 659-7626 With copies to: Shearman & Sterling LLP Broadgate West 9 Appold Street London, United Kingdom EC2A 2AP Attention: Richard J.B. Price Fax: +44 20 7655 5485 and to: Mayer Brown Rowe & Maw LLP 190 South LaSalle Street Chicago, IL 60603 Attention: J. Trent Anderson Fax: (312) 706-8101 2 SECTION 3.2 Benefits of Supplemental Indenture. Nothing expressed or mentioned herein is intended or shall be construed to give any Person, firm or corporation, other than the parties hereto and their successors hereunder and the Holders, any legal or equitable right, remedy or claim under or in respect of this Supplemental Indenture or the Indenture or any provision herein or therein contained. SECTION 3.3 Governing Law. This Supplemental Indenture shall be governed by, and construed in accordance with, the laws of the State of New York. Section 3.4 Ratification of Indenture; Supplemental Indenture Part of Indenture. Except as expressly amended hereby, the Indenture is in all respects ratified and confirmed and all the terms, conditions and provisions thereof shall remain in full force and effect. This Supplemental Indenture shall form a part of the Indenture for all purposes, and every Holder of Notes heretofore or hereafter authenticated and delivered shall be bound hereby. The Trustee makes no representation or warranty as to the validity or sufficiency of this Supplemental Indenture. SECTION 3.5 Counterparts. The parties hereto may sign one or more copies of this Supplemental Indenture in counterparts, all of which together shall constitute one and the same agreement. SECTION 3.6 Headings. The headings of the Articles and the Sections in this Supplemental Indenture are for convenience of reference only and shall not be deemed to alter or affect the meaning or interpretation of any provisions hereof. SECTION 3.7 Trust Indenture Act Controls. If and to the extent that any provision of this Indenture limits, qualifies or conflicts with another provision which is required to be included in this Supplemental Indenture by the TIA, the provision required by the TIA shall control. SECTION 3.8 Severability. In case any provision in this Supplemental Indenture shall be invalid, illegal or unenforceable, the validity, legality and enforceability of the remaining provisions shall not in any way be affected or impaired thereby. SECTION 3.9 Successors. All agreements of ISG in this Supplemental Indenture shall bind its successors. All agreements of the Trustee in this Supplemental Indenture shall bind its successors. [Page Intentionally Left Blank; Signatures Follow] 3 IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be duly executed as of the date first above written. ISPAT INLAND U.L.C., as Issuer By: /s/ Richard Leblanc --------------------------------- Name: Richard Leblanc Title: Secretary MITTAL STEEL USA ISG INC., as Successor Company By: /s/ Carlos M. Hernandez --------------------------------- Name: Carlos M. Hernandez Title: General Counsel and Secretary MITTAL STEEL COMPANY N.V., as Guarantor By: /s/ H.J. Scheffer_ --------------------------------- Name: H.J. Scheffer Title: Company Secretary ISPAT INLAND INC., as Guarantor By: /s/ T.A. McCue --------------------------------- Name: T.A. McCue Title: Treasurer BURNHAM TRUCKING COMPANY, INC., as Guarantor By: /s/ T.A. McCue --------------------------------- Name: T.A. McCue Title: Treasurer INCOAL COMPANY, as Guarantor By: /s/ Marc R. Jeske --------------------------------- Name: M.R. Jeske Title: Secretary ISPAT INLAND MINING COMPANY, as Guarantor By: /s/ T.A. McCue --------------------------------- Name: T.A. McCue Title: Treasurer ISPAT INLAND SERVICE CORP., as Guarantor By: /s/ T.A. McCue --------------------------------- Name: T.A. McCue Title: Treasurer ISPAT INLAND, L.P., as Guarantor By: /s/ Denis Fraser --------------------------------- Name: Denis Fraser Title: Director 3019693 NOVA SCOTIA U.L.C., as Guarantor By: /s/ Richard Leblanc --------------------------------- Name: Richard Leblanc Title: Secretary ISPAT INLAND FINANCE, LLC, as Guarantor By: /s/ T.A. McCue --------------------------------- Name: T.A. McCue Title: Manager LASALLE BANK NATIONAL ASSOCIATION, as Trustee By: /s/ Gregory S. Clarke --------------------------------- Name: Gregory S. Clarke Title: Vice President