Fixed Assets

Fixed assets consisted of the following:



	September 30, 2015			December 31, 2014
Crude oil pipelines and natural gas pipelines and related assets	$	2,481,871		$	466,613
Machinery and equipment	406,512			376,672
Transportation equipment	19,459			18,479
Marine vessels	770,362			731,016
Land, buildings and improvements	41,304			38,037
Office equipment, furniture and fixtures	7,481			6,696
Construction in progress	390,464			222,233
Other	46,456			39,312
Fixed assets, at cost	4,163,909			1,899,058
Less: Accumulated depreciation	(337,087		)	(268,057		)
Net fixed assets	$	3,826,822		$	1,631,001

Our depreciation expense for the periods presented was as follows:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014
Depreciation expense	$	33,716	$	20,736	$	78,265	$	52,422

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, 2014:



ARO liability balance, December 31, 2014	$	14,790
AROs arising from the Enterprise acquisition	158,133
AROs from the consolidation of historical interests in CHOPS and SEKCO	1,988
Accretion Expense	2,781
Settlements	(384		)
ARO liability balance, September 30, 2015	$	177,308

Of the ARO balances disclosed above, $7.7 million is included as current in "Accrued liabilities" on our Unaudited Condensed Consolidated Balance Sheet, as of September 30, 2015. The remainder of the ARO liability as of September 30, 2015, as well as ARO liability as of December 31, 2014, are 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	2015	$	3,420
	2016	$	8,997
	2017	$	9,611
	2018	$	10,291
	2019	$	11,488

Certain of our unconsolidated affiliates have AROs recorded at September 30, 2015 relating to contractual agreements and regulatory requirements. These amounts are immaterial to our Consolidated Financial Statements.