6. INTANGIBLE ASSETS AND LIABILITIES

Our intangible assets resulted from our acquisition, as part of a business combination, of contracts with terms that are favorable to prevailing market prices at the time of acquisition. Amortization of intangible assets recognized in Cost of sales was zero in 2015, $1.2 million in 2014 and $1.7 million in 2013.

Our intangible liabilities resulted from our acquisition, as part of a business combination, of contracts with terms that are unfavorable to prevailing market prices at the time of acquisition. Amortization of intangible liabilities recognized in Revenues was $1.0 million in 2015, 2014, and 2013.

The intangible assets and liabilities are generally amortized straight-line over the life of the related contract. The estimated amortization amounts from intangibles assets and liabilities for each of the next five years as of December 31, 2015 are as follows:



	Amount of Amortization to Recognize in Revenues		Amount of Amortization to Recognize in Cost of Sales
	(In thousands)
2016	$	1,068	$	2,130
2017	1,068		2,130
2018	1,068		2,130
2019	267		2,105
2020	—		2,096