Fixed Assets, Mineral Leaseholds, and Asset Retirement Obligations

Fixed Assets

Fixed assets, net consisted of the following:



	March 31, 2019			December 31, 2018
Crude oil pipelines and natural gas pipelines and related assets	$	2,918,841		$	2,918,285
Alkali facilities, machinery, and equipment	536,987			533,924
Onshore facilities, machinery, and equipment	639,623			639,023
Transportation equipment	19,415			20,102
Marine vessels	957,846			951,597
Land, buildings and improvements	222,249			222,242
Office equipment, furniture and fixtures	20,505			20,505
Construction in progress	114,856			94,025
Other	41,155			41,155
Fixed assets, at cost	5,471,477			5,440,858
Less: Accumulated depreciation	(1,093,199		)	(1,023,825		)
Net fixed assets	$	4,378,278		$	4,417,033

Mineral Leaseholds

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



	March 31, 2019			December 31, 2018
Mineral leaseholds	$	566,019		$	566,019
Less: Accumulated depletion	(6,858		)	(5,538		)
Mineral leaseholds, net	$	559,161		$	560,481

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



	Three Months Ended March 31,
	2019		2018
Depreciation expense	$	71,672	$	68,428
Depletion expense	1,319		1,137

Asset Retirement Obligations

We record asset retirement obligations ("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, 2018



ARO liability balance, December 31, 2018	$	239,865
Accretion expense	2,220
Settlements	(6,068		)
ARO liability balance, March 31, 2019	$	236,017

Of the ARO balances disclosed above, $86.5 million and $67.5 million is included as current in "Accrued liabilities" on our Unaudited Condensed Consolidated Balance Sheet as of March 31, 2019 and December 31, 2018, respectively. The remainder of the ARO liability as of March 31, 2019 and December 31, 2018 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	2019	$	7,660
	2020	$	10,997
	2021	$	9,313
	2022	$	9,892
	2023	$	10,586

Certain of our unconsolidated affiliates have AROs recorded at March 31, 2019 relating to contractual agreements and regulatory requirements. These amounts are immaterial to our Consolidated Financial Statements.