SECOND AMENDMENT TO MEMBERSHIP INTEREST PURCHASE AGREEMENT

Exhibit 2.1

SECOND AMENDMENT TO

     THIS SECOND AMENDMENT to the Membership Interest Purchase Agreement dated as of March 8, 2009, as amended by the First Amendment to Membership Interest Purchase Agreement dated as of April 6, 2009 (collectively, the “ Purchase Agreement ”), by and between Rio Tinto Sage LLC, a Delaware limited liability company (“ Seller ”), and Arch Coal, Inc., a Delaware corporation (“ Buyer ”), is made and entered into between Seller and Buyer (each a “ Party ” and collectively, the “ Parties ”), as of this 30th day of September, 2009 (the “ Second Amendment ”).

RECITALS

     A. Seller and Buyer entered into the Purchase Agreement in order to sell and transfer the equity interests of Jacobs Ranch to Buyer.

     B. Seller currently directly owns one hundred percent (100%) of the membership interests of Jacobs Ranch.

     C. In order to consummate the Acquisition, Seller has determined that it is in its best interest to revise the ownership structure of Jacobs Ranch through (a) the formation of Jacobs Ranch Holdings I, a Delaware limited liability company qualified to do business in Wyoming and a direct, wholly-owned subsidiary of Seller (“ Jacobs Ranch Holdings I ”); (b) the formation of Jacobs Ranch Holdings II, a Delaware limited liability company qualified to do business in Wyoming, a direct, wholly-owned subsidiary of Jacobs Ranch Holdings I and an indirect subsidiary of Seller (“ Jacobs Ranch Holdings II ”); and (c) the transfer of all of the membership interests of Jacobs Ranch from Seller to Jacobs Ranch Holdings II (the “ Restructure ”). Upon completion of the Restructure, (a) Seller will own one hundred percent (100%) of the membership interests in Jacobs Ranch Holdings I, (b) Jacobs Ranch Holdings I will own one hundred percent of the membership interests of Jacobs Ranch Holdings II, and (c) Jacobs Ranch Holdings II will own 100% of the membership interests of Jacobs Ranch.

     D. As a result of the Restructure, the State of Wyoming Department of Environmental Quality, Land Quality Division, has determined that no further Required Approvals are necessary for (a) Permit to Mine, Permit 271; and (b) License to Mine, License numbers 271-T1-L1, 271-L2, and 271-L3, in respect of the transfer of the membership interests in Jacobs Ranch Holdings I by Seller to Buyer.

     E. The Parties have determined that certain covenants may be impossible or impractical to complete prior to the Closing Date.

     F.  Section 9.8 of the Purchase Agreement provides that the Purchase Agreement may be amended in a writing signed by Buyer and Seller.

     G. The Parties desire to further amend the Purchase Agreement as set forth in this Second Amendment.

AMENDMENT

     NOW, THEREFORE, in consideration of the foregoing and other good and valuable consideration, the receipt and sufficiency of which hereby are acknowledged, and intending to be legally bound hereby, the Parties agree to amend the Purchase Agreement as follows:

     1.  Amendments .

          a. Recital A of the Purchase Agreement hereby is deleted in its entirety and replaced with the following:

     “A. Seller owns one hundred percent (100%) of the outstanding membership interests of Jacobs Ranch Holdings I LLC, a Delaware limited liability company (“ Jacobs Ranch Holdings I ”). Jacobs Ranch Holdings I owns one hundred percent (100%) of the outstanding membership interests of Jacobs Ranch Holdings II LLC, a Delaware limited liability company (“ Jacobs Ranch Holdings II ”). Jacobs Ranch Holdings II owns one hundred percent (100%) of the outstanding membership interests of Jacobs Ranch Coal LLC, a Delaware limited liability company (“ Jacobs Ranch ”). Seller, though its indirect ownership of Jacobs Ranch, owns and operates the Mine and, through its indirect ownership of one hundred percent (100%) of the outstanding membership interests in Jacobs Land & Livestock LLC, a Delaware limited liability company (the “ Subsidiary ”), owns or controls certain Mineral and/or Real Properties (collectively, the “ Business ”).”

          b.  Section 1.1(d) of the Purchase Agreement hereby is deleted in its entirety and replaced with the following:

     “” Arch Coal Supply Agreements ” means the agreements in substantially the forms attached to this Agreement as Exhibit A-1 and Exhibit A-2 .

          c.  Section 1.1(oo) of the Purchase Agreement hereby is deleted in its entirety and replaced with the following:

     “” Equity Interests ” means the membership interests of Jacobs Ranch Holdings I held by Seller.”

          d.  Section 1.1(nnnnn) of the Purchase Agreement hereby is amended by deleting the phrase “ Section 2.6(g) ” and replacing it with “ Section 2.6(f) ”.

          e. Section 2.2 of the Purchase Agreement hereby is amended by deleting the phrase “11:59:59 p.m.” and replacing it with “12:00:01 a.m.”.

          f. The phrase “ending after the Closing Date” is hereby deleted from the second and third lines of Section 3.10(k) of the Purchase Agreement and is hereby replaced with “ending after September 30, 2009.”

          g. The phrase “on or prior to the Closing Date” is hereby deleted from the fourth, fifth and sixth lines of Section 3.10(k) of the Purchase Agreement, the fifth line of Section 3.12(e) of the Purchase Agreement, the second line of Section 5.14(a) of the Purchase Agreement, the fourteenth line of Section 5.14(e) of the Purchase Agreement, the third line of Section 5.14(f) of the Purchase Agreement, the sixth line of Section 5.14(g) of the Purchase Agreement and is hereby replaced with “prior to the Closing Date.”

          h. The phrase “on the Closing Date” is hereby deleted from Section 5.8(b) of the Purchase Agreement, the fifth line of Section 5.14(a) of the Purchase Agreement and is hereby replaced with “immediately prior to the Closing Date.”

          i. The phrase “on the Closing Date” is hereby deleted from the fifth line of Section 5.14(a) of the Purchase Agreement and is hereby replaced with “on September 30, 2009.”

          j. The phrase “up to and including the Closing Date” in the thirteenth line of Section 5.14(a) of the Purchase Agreement is hereby deleted, and is hereby replaced with “up to the Closing Date.”

          k. All references to the phrase “the Closing Date” in Section 5.14(c) and Section 5.14(d) of the Purchase Agreement are hereby deleted and are hereby replaced with “September 30, 2009.”

          l. The phrase “after the Closing Date” in the seventh line of Section 5.8(c) of the Purchase Agreement, the second line of Section 5.14(a) of the Purchase Agreement, the second line of Section 5.14(g) of the Purchase Agreement and the first line of Section 8.2(c) is hereby deleted and is hereby replaced with “on or after the Closing Date.”

          m. The phrase “on or before the Closing Date” is hereby deleted from the third and fourth lines of Section 3.12(e) of the Purchase Agreement, the first line of Section 5.8(d) of the Purchase Agreement, and is hereby replaced with “prior to the Closing Date.”

          n. The phrase “as of the Closing Date” is hereby deleted from Section 1.1(o) of the Purchase Agreement, the second line of Section 5.8(a) of the Purchase Agreement, the third, sixth and eighth lines of Section 5.8(d) and Section 5.8(e) of the Purchase Agreement and is hereby replaced with “as of September 30, 2009.”

          o. The word “Date” in the title of Section 8.7 is hereby deleted.

          p.  Section 2.6(f) of the Purchase Agreement hereby is deleted in its entirety and replaced with the following:

     “(f) the Arch Coal Supply Agreements, executed by Rio Tinto Energy America Inc., a Delaware corporation (“ RTEA ”) or an Affiliate of RTEA, as applicable;”

          q.  Section 2.6(g) of the Purchase Agreement hereby is deleted in its entirety and replaced with the following:

     “(g) the Tire Allocation Assignment, executed by Rio Tinto Energy America Services Company, a Delaware corporation;”

          r.  Section 3.1(c) of the Purchase Agreement hereby is amended by deleting the phrase “, as of the Effective Date,” beginning in the first line thereof.

          s.  Section 3.2(a) of the Purchase Agreement hereby is deleted in its entirety and replaced with the following:

     “(a) Jacobs Ranch Holdings I is a limited liability company formed under the laws the State of Delaware on June 17, 2009. Jacobs Ranch Holdings II is a limited liability company formed under the laws of the State of Delaware on June 17, 2009. The Equity Interests, and the membership interests of Jacob Ranch Holdings II, Jacobs Ranch and the Subsidiary, have been legally and validly issued and all legally required contributions have been made under the applicable Organizational Document of each of the Companies.”

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