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	Arch Coal, Inc.
	By:	/s/ Robert J. Messey
		Name:	Robert J. Messey
		Title:	Senior Vice President and Chief Financial Officer

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Exhibit (a)(1)(D)

THIRD OFFERING CIRCULAR SUPPLEMENT

Arch Coal, Inc.

Offer to Pay a Premium Upon the Conversion

of up to an Aggregate of 2,874,926 Shares of Its

5% Perpetual Cumulative Convertible Preferred Stock

(Liquidation Preference $50.00 Per Share) to Common Stock

CUSIP No. 039380 20 9

ISIN No. US0393802097

     This third offering circular supplement relates to the offer by Arch Coal, Inc., a Delaware corporation (the “Company”), to pay a premium to holders of any and all of its outstanding 5% Perpetual Cumulative Convertible Preferred Stock (Liquidation Preference $50.00 Per Share) (“Preferred Stock”) who elect to convert their shares of Preferred Stock to the Company’s Common Stock, $.01 par value (“Common Stock”), in accordance with the terms of the Preferred Stock and upon the terms and subject to the conditions set forth in the Company’s offering circular, dated November 30, 2005 (the “Offering Circular”), the offering circular supplement, dated December 5, 2005 (the “First Offering Circular Supplement”), the offering circular supplement, dated December 13, 2005 (the “Second Offering Circular Supplement”) and in the accompanying letter of transmittal. This third offering circular supplement further updates the Offering Circular, the First Offering Circular Supplement, the Second Offering Circular Supplement and should be read in conjunction with the Offering Circular, the First Offering Circular Supplement and the Second Offering Circular Supplement.

     The Company has determined to change the formula set forth in the First Offering Circular for calculating the number of shares that will be paid as a premium in the conversion offer for each share of Preferred Stock validly tendered and accepted for conversion and to extend the conversion offer. As changed, the premium offered in the conversion offer is an amount of shares of our Common Stock valued at $3.50, as determined by dividing (i) $3.50 by (ii) the volume-weighted average of the reported sales prices on the New York Stock Exchange of our Common Stock during the 10 trading days ending at the close of the second trading day prior to the expiration of the conversion offer (including any extension), per share of Preferred Stock validly tendered and accepted for conversion. As extended, the conversion offer will expire at 12:00 midnight, New York City time, on December 30, 2005, unless extended or earlier terminated. Other than this change to the formula used to determine the number of shares of Common Stock that you will receive as a premium if you participate in the conversion offer and the extension of the conversion offer, the terms and conditions set forth in the Offering Circular, the First Offering Circular Supplement and the Second Offering Circular Supplement remain in effect. As indicated in the Second Offering Circular Supplement, holders of Preferred Stock who wish to request an estimate of the number of shares of Common Stock that would constitute the premium paid in the conversion offer, per share of Preferred Stock validly tendered and accepted for conversion, assuming that the conversion offer expired at midnight on the date prior to the date of inquiry, may request such information from American Stock Transfer & Trust Company, the information agent with respect to the conversion offer, toll-free at (877) 248-6417.

     In addition to the Company’s financial information contained or incorporated by reference in the Offering Circular, the Company is providing the following additional financial information. The Company’s book value per common share as of September 30, 2005 was $18.09. In addition, below is the Company’s income per common share from continuing operations, basic and diluted, and ratio of earnings to combined fixed charges and preference dividends for the periods indicated.

     With respect to the information set forth under the caption “Interests of Directors and Officers” in the Offering Circular, we amend and restate such information in its entirety as set forth below:

     Enclosed is a new letter of transmittal for your Preferred Stock. If you have not already returned a completed letter of transmittal with respect to your Preferred Stock, please complete the enclosed letter of transmittal. If you have already returned a completed letter of transmittal, you do not need to return the enclosed letter of transmittal unless you wish to change the information set forth in the letter of transmittal that you have already returned. This new letter of transmittal, when received, will supersede your earlier letter of transmittal. In any event, you may validly withdraw shares of Preferred Stock that you have already tendered or that you may tender at any time prior to the expiration date of the conversion offer. In addition, if not previously returned, you may withdraw any shares of Preferred Stock that you tender that are not accepted by us for conversion before January 30, 2006, which is 40 business days from the commencement of the conversion offer. For a withdrawal of shares of Preferred Stock to be effective, you must comply with the appropriate procedures of DTC’s ATOP system prior to the expiration date or, if not accepted by us before January 30, 2006, the 40th business day after the commencement of the conversion offer. Any notice of withdrawal must identify the shares of Preferred Stock to be withdrawn, including the name and number of the account at DTC to be credited and otherwise comply with the procedures of DTC.

     If you have questions regarding the procedures for tendering in the conversion offer or require assistance in tendering your shares of Preferred Stock, please contact American Stock Transfer & Trust Company, the information agent for the conversion offer, toll-free at (877) 248-6417 or (718) 921-8317. You may also contact the information agent toll-free at (877) 248-6417 to receive an estimate of the number of shares of Common Stock that would constitute the premium paid in the conversion offer per share of Preferred Stock validly tendered and accepted for conversion, assuming that the conversion offer expired on the date of inquiry. If you would like additional copies of this offering circular supplement, the Offering Circular or any supplement thereto, our annual, quarterly and current reports, proxy statement and other information that we incorporate by reference in the Offering Circular, please contact either the information agent at either telephone number set forth above or Investor Relations at Arch Coal at (314) 994-2700. Holders of Preferred Stock may also contact their brokers, dealers, commercial banks, trust companies or other nominees through which they hold their Preferred Stock with questions and requests for assistance.

     The date of this third offering circular supplement is December 16, 2005.

Exhibit (a)(1)(F)

ARCH COAL, INC.

LETTER TO THE DEPOSITORY TRUST COMPANY PARTICIPANTS

Offer to Pay a Premium Upon the Conversion

of up to an Aggregate of 2,874,926 Shares of Its

5% Perpetual Cumulative Convertible Preferred Stock

(Liquidation Preference $50.00 Per Share)

CUSIP No. 039380 20 9

ISIN No. US0393802097

Pursuant to the Offering Circular dated November 30, 2005

and the Offering Circular Supplement dated December 5, 2005

SHARES OF 5% PERPETUAL CUMULATIVE CONVERTIBLE PREFERRED STOCK (LIQUIDATION PREFERENCE $50.00 PER SHARE) (“PREFERRED STOCK”) TENDERED IN THE CONVERSION OFFER MAY BE WITHDRAWN AT ANY TIME PRIOR TO THE EXPIRATION DATE (AS IT MAY BE EXTENDED). IN ADDITION, YOU MAY WITHDRAW ANY TENDERED SHARES OF PREFERRED STOCK AFTER JANUARY 30, 2006, IF WE HAVE NOT ACCEPTED THEM FOR CONVERSION.

To Depository Trust Company Participants:

      We are enclosing herewith the documents listed below relating to the offer by Arch Coal, Inc., a Delaware corporation (the “Company”), to pay a premium to holders of any and all of the outstanding Preferred Stock who elect to convert their shares of Preferred Stock to the Company’s Common Stock, $.01 par value (“Common Stock”), in accordance with the terms of the Preferred Stock and upon the terms and subject to the conditions set forth in the Company’s Offering Circular, dated November 30, 2005 (the “Offering Circular”), in the Company’s Offering Circular Supplement, dated December 5, 2005, the Company’s Second Offering Circular Supplement, dated December 13, 2005, the Company’s Third Offering Circular, dated December 16, 2005 (collectively, the “Offering Circular Supplements”), and in the accompanying letter of transmittal (the “Letter of Transmittal”). The premium offered in this conversion offer is an amount of shares of our Common Stock valued at $3.50, as determined by dividing (i) $3.50 by (ii) the volume-weighted average of the reported sales prices on the New York Stock Exchange of our Common Stock during the 10 trading days ending at the close of the second trading day prior to the expiration of this conversion offer (including any extension), per share of Preferred Stock validly tendered and accepted for conversion. Holders who validly tender shares of Preferred Stock for conversion will receive the premium in addition to the number of shares of Common Stock issuable upon conversion pursuant to the conversion terms of the Preferred Stock. As of the date of the Offering Circular, the conversion ratio for the Preferred Stock was 2.3985 shares of our Common Stock for each share of Preferred Stock validly converted. On November 29, 2005, 2,874,926 shares of our Preferred Stock were outstanding. Certain terms used but not defined herein have the meanings ascribed to them in the Offering Circular.

      The Company is requesting that you contact your clients for whom you hold shares of our Preferred Stock through your account with The Depository Trust Company (“DTC”) regarding the Conversion Offer. For

your information and for forwarding to your clients for whom you hold shares of our Preferred Stock through your DTC account, enclosed herewith are copies of the following documents:

      1. Offering Circular and Offering Circular Supplements;

      We urge you to contact your clients promptly. Please note that the Conversion Offer will expire on the Expiration Date, unless extended or earlier terminated. The Conversion Offer is subject to certain conditions. Please see the section of the Offering Circular entitled “The Conversion Offer — Conditions to the Conversion Offer.”

      To participate in the Conversion Offer, a duly executed and properly completed Letter of Transmittal (or facsimile thereof or agent’s message in lieu thereof), with any required signature guarantees and any other required documents, should be sent to the conversion agent, and the book-entry transfer procedures should be complied with, all in accordance with the instructions set forth in the Letter of Transmittal and the Offering Circular.

      The Company will not pay any fee, commission or expense to any broker or dealer or to any other persons (other than the dealer manager, the exchange agent and the information agent) in connection with the solicitation of tenders of shares of Preferred Stock pursuant to the Conversion Offer.

      Additional copies of the enclosed materials may be obtained from the conversion agent by calling American Stock Transfer & Trust Company at (877) 248-6417.

Very truly yours,

ARCH COAL, INC.

      NOTHING HEREIN OR IN THE ENCLOSED DOCUMENTS SHALL CONSTITUTE YOU OR ANY PERSON AS AN AGENT OF THE COMPANY OR THE CONVERSION AGENT, OR AUTHORIZE YOU OR ANY OTHER PERSON TO USE ANY DOCUMENT OR MAKE ANY STATEMENTS ON BEHALF OF EITHER OF THEM WITH RESPECT TO THE CONVERSION OFFER, EXCEPT FOR STATEMENTS EXPRESSLY MADE IN THE OFFERING CIRCULAR OR THE ACCOMPANYING LETTER OF TRANSMITTAL.

Exhibit (a)(1)(G)

ARCH COAL, INC.

LETTER TO CLIENTS

Offer To Pay a Premium Upon The Conversion

of up to an Aggregate of 2,874,926 Shares of Its

5% Perpetual Cumulative Convertible Preferred Stock

(Liquidation Preference $50.00 Per Share)

CUSIP No. 039380 20 9

ISIN No. US0393802097

Pursuant to the Offering Circular dated November 30, 2005,

the Offering Circular Supplement dated December 5, 2005,

the Second Offering Circular Supplement dated December 13, 2005

and the Third Offering Circular Supplement dated December 16, 2005

SHARES OF 5% PERPETUAL CUMULATIVE CONVERTIBLE PREFERRED STOCK (LIQUIDATION PREFERENCE $50.00 PER SHARE) (“PREFERRED STOCK”) TENDERED IN THE CONVERSION OFFER MAY BE WITHDRAWN AT ANY TIME PRIOR TO THE EXPIRATION DATE (AS IT MAY BE EXTENDED). IN ADDITION, YOU MAY WITHDRAW ANY TENDERED SHARES OF PREFERRED STOCK AFTER JANUARY 30, 2006, IF WE HAVE NOT ACCEPTED THEM FOR CONVERSION.

To Our Clients:

      We are enclosing herewith an Offering Circular, dated November 30, 2005 (the “Offering Circular”), and an Offering Circular Supplement, dated December 5, 2005, a Second Offering Circular Supplement, dated December 13, 2005 and a Third Offering Circular dated December 16, 2005 (collectively, the “Offering Circular Supplements”), of Arch Coal, Inc., a Delaware corporation (the “Company”), and a letter of transmittal (the “Letter of Transmittal”) relating to the offer by the Company to pay a premium to holders of any and all of the outstanding Preferred Stock who elect to convert their shares of Preferred Stock to the Company’s Common Stock, $.01 par value (“Common Stock”), in accordance with the terms of the Preferred Stock and upon the terms and subject to the conditions set forth in the Offering Circular, the Offering Circular Supplements and the accompanying Letter of Transmittal. The premium offered in this conversion offer is an amount of shares of the Company’s Common Stock valued at $3.50, as determined by dividing (i) $3.50 by (ii) the volume-weighted average of the reported sales prices on the New York Stock Exchange of the Company’s Common Stock during the 10 trading days ending at the close of the second trading day prior to the expiration of this conversion offer (including any extension), per share of Preferred Stock validly tendered and accepted for conversion. Holders who validly tender shares of Preferred Stock for conversion will receive the premium in addition to the number of shares of Common Stock issuable upon conversion pursuant to the conversion terms of the Preferred Stock. As of the date of the Offering Circular, the conversion ratio for the Preferred Stock was 2.3985 shares of the Company’s Common Stock for each share of Preferred Stock validly converted. On November 29, 2005, 2,874,926 shares of the Company’s Preferred Stock were outstanding. Certain terms used but not defined herein have the meanings ascribed to them in the Offering Circular.

      The Conversion Offer is subject to certain conditions. See the section of the Offering Circular entitled “The Conversion Offer — Conditions to the Conversion Offer.”

      We are the holder of your shares of Preferred Stock through our account with the Depository Trust Company (“DTC”). A tender of such shares of Preferred Stock can be made only by us as a DTC participant

and pursuant to your instructions. The enclosed Letter of Transmittal is furnished to you for your information only and cannot be used by you to tender shares of Preferred Stock held by us for your account.

      We request instructions as to whether you wish to tender any or all of the shares of Preferred Stock held by us through our DTC account pursuant to the terms and conditions set forth in the Offering Circular, the Offering Circular Supplements and the Letter of Transmittal.

      We urge you to read the Offering Circular, including the documents incorporated by reference therein, the Offering Circular Supplements and the Letter of Transmittal carefully before instructing us to tender your shares of Preferred Stock. You may use the attached form to give your instructions.

PLEASE RETURN YOUR INSTRUCTIONS TO US IN THE ENCLOSED ENVELOPE OR CONTACT YOUR REPRESENTATIVE WITH INSTRUCTIONS TO PERMIT US TO TENDER YOUR SHARES OF PREFERRED STOCK PRIOR TO THE EXPIRATION DATE.

INSTRUCTIONS TO THE DEPOSITORY TRUST COMPANY PARTICIPANT

To the Participant of The Depository Trust Company:

     The undersigned hereby acknowledges receipt of the Offering Circular, dated November 30, 2005 (the “Offering Circular”), and the Offering Circular Supplement, dated December 5, 2005 the Second Offering Circular Supplement, dated December 13, 2005, and the Third Offering Circular Supplement, dated December 16, 2005 (collectively, the “Offering Circular Supplements”), of Arch Coal, Inc., a Delaware corporation (the “Company”), and the Letter of Transmittal, which together set forth the terms and conditions of the offer (the “Conversion Offer”) by the Company to pay a premium to holders of any and all of the Company’s outstanding 5% Perpetual Cumulative Convertible Preferred Stock (Liquidation Preference $50.00 Per Share) (“Preferred Stock”) who elect to convert their shares of Preferred Stock to shares of the Company’s Common Stock, $0.01 par value (“Common Stock”), in accordance with the terms of the Preferred Stock and upon the terms and subject to the conditions set forth in the Offering Circular, the Offering Circular Supplements and in the Letter of Transmittal. Certain terms used but not defined herein have the meanings ascribed to them in the Offering Circular.

     This will instruct you as to the action to be taken by you, for the account of the undersigned, relating to the Conversion Offer.

     With respect to the Conversion Offer, the undersigned hereby instructs you (check appropriate box):

     The undersigned represents that either (i) upon the conversion of the shares of Preferred Stock tendered pursuant to the Conversion Offer, the undersigned will not beneficially own in excess of 9.9% of the aggregate number of shares of the Company’s Common Stock outstanding immediately after giving effect to such conversion or (ii) these instructions set forth (a) the number of shares of Common Stock that the undersigned will beneficially own at the time of the conversion of the tendered shares of Preferred Stock, excluding shares issued upon conversion of shares of Preferred Stock in the Conversion Offer, (b) the number of shares of Preferred Stock the Participant is instructed to tender hereby, and (c) the number of shares of Preferred Stock being tendered through other Participants, and that the undersigned is requesting that the Company does not accept for conversion any shares of Preferred Stock to the extent that upon conversion of such shares of Preferred Stock the undersigned’s beneficial ownership of the Company’s Common Stock will exceed 9.9% of the aggregate number of shares of the Company’s Common Stock outstanding following the Conversion Offer.

SIGN HERE

Name(s) of beneficial owner(s):

Signature(s):

Name(s):

(Please Print)

Address(es):

Telephone Number(s):

Taxpayer Identification or

Social Security Number(s):

Date: