8-K

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the
Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): December 29, 2005 (December 29, 2005)

Arch Coal, Inc.

(Exact name of registrant as specified in its charter)

Delaware	1-13105	43-0921172
(State or other jurisdiction of incorporation)	(Commission File Number)	(I.R.S. Employer Identification No.)

CityPlace One, Suite 300, St. Louis, Missouri 63141

(Address of principal executive offices) (Zip code)

Registrant’s telephone number, including area code: (314) 994-2700

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

o Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

o Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

o Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

o Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

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Exhibit Index begins on page 4.

Item 8.01 Other Events.

     On December 29, 2005, Arch Coal, Inc. announced the conclusion of the conversion price determination period and the results of the premium calculation for the previously announced conversion offer relating to its 5% Perpetual Cumulative Convertible Preferred Stock (Liquidation Preference $50.00 Per Share). A copy of Arch Coal, Inc.’s press release is attached hereto as Exhibit 99.1.

Item 9.01 Financial Statements and Exhibits.

     (c) Exhibits.

     The following Exhibit is filed with this Current Report on Form 8-K:

Exhibit No.	Description
99.1	Press Release dated December 29, 2005

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Exhibit Index begins on page 4.

SIGNATURES

     Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Dated: December 29, 2005	ARCH COAL, INC
	By:	/s/ Robert G. Jones
		Robert G. Jones
		Vice President -- Law, General Counsel and Secretary

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Exhibit Index begins on page 4.

EXHIBIT INDEX

Exhibit No.	Description
99.1	Press Release dated December 29, 2005.

Page 4 of 4 pages.

EX-99.1

Exhibit 99.1
 

News from
Arch Coal, Inc.

FOR FURTHER INFORMATION:
Media — Kim Link (314) 994-2936

FOR IMMEDIATE RELEASE
December 29, 2005

Arch Coal Announces Conclusion of the Conversion Price
Determination Period for Its Conversion Offer

     ST. LOUIS (December 29, 2005) — Arch Coal, Inc. (NYSE: ACI) today announced that the determination period for the conversion premium to be paid in connection with the company’s conversion offer for its 5% Perpetual Cumulative Convertible Preferred Stock has concluded. Each share of preferred stock validly tendered and accepted for conversion will be converted into an aggregate of 2.4424 shares of the company’s common stock, which includes a conversion premium of .0439 shares. The conversion premium represents the amount of shares of common stock determined by dividing (i) $3.50 by (ii) $79.65, the volume-weighted average of the reported sales prices on the New York Stock Exchange of the company’s common stock during the ten trading days from Wednesday, December 14, 2005 through Wednesday, December 28, 2005.

     On December 1, 2005, Arch commenced an offer to pay a premium to holders of any and all of its 5% Perpetual Cumulative Convertible Preferred Stock who elect to convert their preferred stock to shares of the company’s common stock subject to the terms of the offer. The offer is scheduled to expire at 12:00 midnight, Eastern Standard Time, on Friday, December 30, 2005. If all shares of preferred stock that were outstanding as of the commencement of the offer were validly tendered and accepted for conversion, Arch would issue an aggregate of approximately 6,895,510 shares of common stock pursuant to the conversion terms of the preferred stock, plus an aggregate conversion premium of approximately 126,209 shares of common stock.

     The offer is being made pursuant to an offering circular dated November 30, 2005, an offering circular supplement dated December 5, 2005, a second offering circular supplement dated December 13, 2005, a third offering circular supplement dated December 16, 2005 and related documents. The completion of the offer is subject to conditions described in the conversion offer documents.

     This press release is not an offer to convert, or a solicitation of an offer to convert, any preferred stock. The conversion offer is being made only on the terms and subject to the conditions described in the offering circular, the offering circular supplements and related documents. Copies of the offering circular, the offering circular supplements and related documents have been filed with the Securities and Exchange Commission as exhibits to a Schedule TO. Holders of preferred stock may address questions about the conversion offer or requests for copies of the offering circular, the offering circular supplements and related documents to American Stock Transfer & Trust Company by calling toll-free at (800) 937-5449.

     St. Louis-based Arch Coal is the nation’s second largest coal producer, with subsidiary operations in West Virginia, Kentucky, Virginia, Wyoming, Colorado and Utah. Through these operations, Arch provides the fuel for approximately 7% of the electricity generated in the United States.

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