Guarantees	9 Months Ended
Sep. 30, 2011
Guarantees
Guarantees	16. Guarantees The Company has agreed to continue to provide surety bonds and letters of credit for the reclamation and retiree healthcare obligations of Magnum Coal Company ("Magnum") related to the properties the Company sold to Magnum on December 31, 2005. Patriot Coal Corporation ("Patriot") acquired Magnum in July 2008. The purchase agreement requires Magnum to reimburse the Company for costs related to the surety bonds and letters of credit and to use commercially reasonable efforts to replace the obligations. If the surety bonds and letters of credit related to the reclamation obligations are not replaced by Magnum within a specified period of time, Magnum must post a letter of credit in favor of the Company in the amounts of the reclamation obligations. As of September 30, 2011, Patriot has replaced $48.9 million of the surety bonds and has posted letters of credit of $32.7 million in the Company's favor. At September 30, 2011, the Company had $38.5 million of surety bonds remaining related to properties sold to Magnum. The surety bonding amounts are mandated by the state and are not directly related to the estimated cost to reclaim the properties. Magnum also acquired certain coal supply contracts with customers who have not consented to the contracts' assignment from the Company to Magnum. The Company has committed to purchase coal from Magnum to sell to those customers at the same price it is charging the customers for the sale. In addition, certain contracts were assigned to Magnum, but the Company has guaranteed Magnum's performance under the contracts. The longest of the coal supply contracts extends to the year 2017. If Magnum is unable to supply the coal for these coal sales contracts then the Company would be required to purchase coal on the open market or supply contracts from its existing operations. At market prices effective at September 30, 2011, the cost of purchasing 10.3 million tons of coal to supply the contracts that have not been assigned over their duration would exceed the sales price under the contracts by approximately $264.3 million, and the cost of purchasing 0.9 million tons of coal to supply the assigned and guaranteed contracts over their duration would exceed the sales price under the contracts by approximately $19.5 million. As the Company does not believe that it is probable that it would have to purchase replacement coal, no losses have been recorded in the consolidated financial statements as of September 30, 2011. However, if the Company would have to perform under these guarantees, it could potentially have a material adverse effect on the business, results of operations and financial condition of the Company. In connection with the Company's acquisition of the coal operations of Atlantic Richfield Company (ARCO) and the simultaneous combination of the acquired ARCO operations and the Company's Wyoming operations into the Arch Western joint venture, the Company agreed to indemnify the other member of Arch Western against certain tax liabilities in the event that such liabilities arise prior to June 1, 2013 as a result of certain actions taken, including the sale or other disposition of certain properties of Arch Western, the repurchase of certain equity interests in Arch Western by Arch Western or the reduction under certain circumstances of indebtedness incurred by Arch Western in connection with the acquisition. If the Company were to become liable, the maximum amount of potential future tax payments is $22.3 million at September 30, 2011, which is not recorded as a liability in the Company's condensed consolidated financial statements. Since the indemnification is dependent upon the initiation of activities within the Company's control and the Company does not intend to initiate such activities, it is remote that the Company will become liable for any obligation related to this indemnification. However, if such indemnification obligation were to arise, it could potentially have a material adverse effect on the business, results of operations and financial condition of the Company.

16. Guarantees

The Company has agreed to continue to provide surety bonds and letters of credit for the reclamation and retiree healthcare obligations of Magnum Coal Company ("Magnum") related to the properties the Company sold to Magnum on December 31, 2005. Patriot Coal Corporation ("Patriot") acquired Magnum in July 2008. The purchase agreement requires Magnum to reimburse the Company for costs related to the surety bonds and letters of credit and to use commercially reasonable efforts to replace the obligations. If the surety bonds and letters of credit related to the reclamation obligations are not replaced by Magnum within a specified period of time, Magnum must post a letter of credit in favor of the Company in the amounts of the reclamation obligations. As of September 30, 2011, Patriot has replaced $48.9 million of the surety bonds and has posted letters of credit of $32.7 million in the Company's favor. At September 30, 2011, the Company had $38.5 million of surety bonds remaining related to properties sold to Magnum. The surety bonding amounts are mandated by the state and are not directly related to the estimated cost to reclaim the properties.

Magnum also acquired certain coal supply contracts with customers who have not consented to the contracts' assignment from the Company to Magnum. The Company has committed to purchase coal from Magnum to sell to those customers at the same price it is charging the customers for the sale. In addition, certain contracts were assigned to Magnum, but the Company has guaranteed Magnum's performance under the contracts. The longest of the coal supply contracts extends to the year 2017. If Magnum is unable to supply the coal for these coal sales contracts then the Company would be required to purchase coal on the open market or supply contracts from its existing operations. At market prices effective at September 30, 2011, the cost of purchasing 10.3 million tons of coal to supply the contracts that have not been assigned over their duration would exceed the sales price under the contracts by approximately $264.3 million, and the cost of purchasing 0.9 million tons of coal to supply the assigned and guaranteed contracts over their duration would exceed the sales price under the contracts by approximately $19.5 million. As the Company does not believe that it is probable that it would have to purchase replacement coal, no losses have been recorded in the consolidated financial statements as of September 30, 2011. However, if the Company would have to perform under these guarantees, it could potentially have a material adverse effect on the business, results of operations and financial condition of the Company.

In connection with the Company's acquisition of the coal operations of Atlantic Richfield Company (ARCO) and the simultaneous combination of the acquired ARCO operations and the Company's Wyoming operations into the Arch Western joint venture, the Company agreed to indemnify the other member of Arch Western against certain tax liabilities in the event that such liabilities arise prior to June 1, 2013 as a result of certain actions taken, including the sale or other disposition of certain properties of Arch Western, the repurchase of certain equity interests in Arch Western by Arch Western or the reduction under certain circumstances of indebtedness incurred by Arch Western in connection with the acquisition. If the Company were to become liable, the maximum amount of potential future tax payments is $22.3 million at September 30, 2011, which is not recorded as a liability in the Company's condensed consolidated financial statements. Since the indemnification is dependent upon the initiation of activities within the Company's control and the Company does not intend to initiate such activities, it is remote that the Company will become liable for any obligation related to this indemnification. However, if such indemnification obligation were to arise, it could potentially have a material adverse effect on the business, results of operations and financial condition of the Company.