Fixed Assets and Mineral Leaseholds

Fixed Assets

Fixed assets consisted of the following:



	March 31, 2018			December 31, 2017
Crude oil pipelines and natural gas pipelines and related assets	$	3,081,841		$	3,028,657
Alkali facilities, machinery, and equipment	499,539			497,601
Onshore facilities, machinery, and equipment	725,217			692,364
Transportation equipment	21,468			21,483
Marine vessels	934,315			918,953
Land, buildings and improvements	224,055			223,186
Office equipment, furniture and fixtures	18,162			18,112
Construction in progress	96,800			151,768
Other	51,483			48,891
Fixed assets, at cost	5,652,880			5,601,015
Less: Accumulated depreciation	(802,261		)	(734,986		)
Net fixed assets	$	4,850,619		$	4,866,029

Mineral Leaseholds

Our Mineral Leaseholds, as relating to our recently acquired Alkali Business, consist of the following:



	March 31, 2018			December 31, 2017
Mineral leaseholds	566,019			566,019
Less: Accumulated depletion	(2,650		)	(1,513		)
Mineral leaseholds, net	$	563,369		$	564,506

Our depreciation and depletion expense for the periods presented was as follows:



	Three Months Ended March 31,
	2018		2017
Depreciation expense	$	68,428	$	49,924
Depletion expense	1,137		—

Asset Retirement Obligations

We record AROs in connection with legal requirements to perform specified retirement activities under contractual arrangements and/or governmental regulations.

The following table presents information regarding our AROs since December 31, 2017:



ARO liability balance, December 31, 2017	$	198,187
Accretion expense	2,718
Change in estimate	1,163
Settlements	(2,836		)
ARO liability balance, March 31, 2018	$	199,232

Of the ARO balances disclosed above, $11.8 million and $20.9 million is included as current in "Accrued liabilities" on our Unaudited Condensed Consolidated Balance Sheet as of March 31, 2018 and December 31, 2017, respectively. The remainder of the ARO liability as of March 31, 2018 and December 31, 2017 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	2018	$	8,264
	2019	$	9,908
	2020	$	8,743
	2021	$	9,337
	2022	$	9,972

Certain of our unconsolidated affiliates have AROs recorded at March 31, 2018 relating to contractual agreements and regulatory requirements. These amounts are immaterial to our Consolidated Financial Statements.