Note 3. Inventories

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

	March 31, 2017		December 31, 2016
NGLs	$	1,107.5	$	1,156.1
Petrochemicals and refined products		474.2		220.7
Crude oil		319.5		360.0
Natural gas		20.8		33.7
Total	$	1,922.0	$	1,770.5

Inventories of petrochemicals and refined products increased since December 31, 2016 primarily due to our marketing group acquiring additional volumes during the first quarter of 2017 to take advantage of contango opportunities using our storage assets. These contango positions are expected to settle during the second quarter of 2017. Inventories of our other products decreased since December 31, 2016 primarily due to the settlement of contango positions in these products during the first quarter of 2017.

Due to fluctuating commodity prices, we recognize lower of cost or market 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 March 31,
	2017		2016
Cost of sales (1)	$	5,335.7	$	3,208.3
Lower of cost or net realizable value adjustments within cost of sales		3.4		5.3

(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.