Inventories

The following schedule presents a summary of inventories by major class:



	March 31, 2012								December 31, 2011
(Millions of dollars)	LIFO			Non- LIFO		Total			LIFO			Non- LIFO		Total

At the lower of cost, determined on the FIFO or weighted-average cost methods, or market:
Raw materials	$	159		$	343	$	502		$	163		$	334	$	497
Work in process	212			125		337			245			126		371
Finished goods	662			787		1,449			708			760		1,468
Supplies and other	—			305		305			—			300		300
	1,033			1,560		2,593			1,116			1,520		2,636
Excess of FIFO or weighted-average cost over LIFO cost	(239		)	—		(239		)	(280		)	—		(280		)
Total	$	794		$	1,560	$	2,354		$	836		$	1,520	$	2,356

We use the LIFO method of valuing inventory for financial reporting purposes for most U.S. inventories. Interim LIFO calculations are based on management’s estimates of expected year-end inventory levels and costs. An actual valuation of inventory under the LIFO method is made at the end of each year based on the inventory levels and costs at that time.