5. Inventories

Inventories are valued at the lower of cost or market for last-in, first-out (“LIFO”) inventory and lower of cost or net realizable value for first-in, first-out (“FIFO”) inventory. Approximately 30 percent of our inventories are valued using the LIFO method of determining cost. All other inventories are valued at the FIFO method of determining cost. An actual valuation of inventory under the LIFO method can be made only at the end of each year based on inventory levels and costs at that time. Accordingly, interim LIFO calculations must necessarily be based on management’s estimates of expected year-end inventory levels and costs. Because these are based on estimates, interim results are subject to change in the final year-end LIFO inventory valuation. The estimated interim LIFO adjustment in each period was not material and therefore, no adjustment was recorded for the three months ended March 31, 2018 or March 31, 2017.

Inventories consist of the following:

	March 31,		December 31,
	2018		2017
Finished and in-process products	$	32,200	$	31,307
Raw materials and supplies		15,640		15,859
	$	47,840	$	47,166