Note 3. Inventories

Our inventory amounts by product type were as follows at the dates indicated:

	June 30, 2018		December 31, 2017
NGLs	$	1,120.2	$	917.4
Petrochemicals and refined products		189.0		161.5
Crude oil		410.0		516.3
Natural gas		10.4		14.6
Total	$	1,729.6	$	1,609.8

Due to fluctuating commodity prices, we recognize lower of cost or net realizable value adjustments when the carrying value of our available-for-sale inventories exceeds their net realizable value. The following table presents our total cost of sales amounts and lower of cost or net realizable value adjustments for the periods indicated:

	For the Three Months Ended June 30,				For the Six Months Ended June 30,
	2018		2017		2018		2017
Cost of sales (1)	$	6,391.9	$	4,731.1	$	13,532.3	$	10,066.8
Lower of cost or net realizable value adjustments recognized within cost of sales		0.7		2.6		2.6		6.0

(1) Cost of sales is a component of “Operating costs and expenses” as presented on our Unaudited Condensed Statements of Consolidated Operations. Fluctuations in these amounts are primarily due to changes in energy commodity prices and sales volumes associated with our marketing activities.