Inventory

12 Months Ended

Dec. 31, 2011

INVENTORY

2. INVENTORY

As of December 31, 2011, 81% of the Company's inventory was valued using average cost, 17% was determined using the FIFO method and the remaining inventory was valued using the specific identification method. The following table summarizes our inventory balances as of December 31, 2011 and 2010:

	December 31,
	2011		2010
	(in millions)
Coal, fuel oil and other raw materials	$	444	$	272
Spare parts and supplies		341		277
Total	$	785	$	549