Note 3. Inventories

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

	September 30, 2017		December 31, 2016
NGLs	$	1,527.8	$	1,156.1
Petrochemicals and refined products		223.4		220.7
Crude oil		211.9		360.0
Natural gas		20.1		33.7
Total	$	1,983.2	$	1,770.5

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 September 30,				For the Nine Months Ended September 30,
	2017		2016		2017		2016
Cost of sales (1)	$	5,049.6	$	4,088.6	$	15,116.4	$	11,135.6
Lower of cost or net realizable value adjustments within cost of sales		1.7		1.5		7.7		7.6

(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.