Fixed Assets

Fixed assets consisted of the following:



	September 30, 2016			December 31, 2015
Crude oil pipelines and natural gas pipelines and related assets	$	2,667,221		$	2,501,821
Machinery and equipment	419,355			414,100
Transportation equipment	18,639			19,025
Marine vessels	842,700			794,508
Land, buildings and improvements	49,465			41,202
Office equipment, furniture and fixtures	9,441			7,540
Construction in progress	653,949			485,575
Other	46,915			46,455
Fixed assets, at cost	4,707,685			4,310,226
Less: Accumulated depreciation	(509,419		)	(378,247		)
Net fixed assets	$	4,198,266		$	3,931,979

Our depreciation expense for the periods presented was as follows:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2016		2015		2016		2015
Depreciation expense	$	46,909	$	33,716	$	135,428	$	78,265

Asset Retirement Obligations

We record AROs in connection with legal requirements to perform specified retirement activities under contractual arrangements and/or governmental regulations. As a result of the Enterprise acquisition of the offshore pipeline and services business of Enterprise Products Partners, L.P. on July 24, 2015, we recorded AROs based on the fair value measurement assigned during the preliminary purchase price allocation.

The following table presents information regarding our AROs since December 31, 2015:



ARO liability balance, December 31, 2015	$	188,662
AROs arising from the purchase of the remaining interest in Deepwater Gateway	10,470
AROs from the consolidation of historical interest in Deepwater Gateway	10,470
Accretion expense	7,918
Change in estimate	5,609
Settlements	(3,216		)
ARO liability balance, September 30, 2016	$	219,913

Of the ARO balances disclosed above, $5.2 million and $9.8 million is included as current in "Accrued liabilities" on our Unaudited Condensed Consolidated Balance Sheet as of September 30, 2016 and December 31, 2015, respectively. The remainder of the ARO liability as of September 30, 2016 and December 31, 2015 is included in "Other long-term liabilities" on our Unaudited Condensed Consolidated Balance Sheet.

With respect to our AROs, the following table presents our forecast of accretion expense for the periods indicated:



Remainder of	2016	$	2,710
	2017	$	9,807
	2018	$	8,144
	2019	$	8,735
	2020	$	9,298

Certain of our unconsolidated affiliates have AROs recorded at September 30, 2016 relating to contractual agreements and regulatory requirements. These amounts are immaterial to our Consolidated Financial Statements.