4. Fixed Assets and Asset Retirement Obligations

Fixed Assets

Fixed assets consisted of the following:



	September 30, 2012			December 31, 2011
Pipelines and related assets	$	218,155		$	167,865
Machinery and equipment	63,091			46,233
Transportation equipment	20,280			21,732
Marine vessels	297,416			262,216
Land, buildings and improvements	14,037			13,140
Office equipment, furniture and fixtures	4,487			3,778
Construction in progress	53,135			14,236
Other	14,062			11,938
Fixed assets, at cost	684,663			541,138
Less: Accumulated depreciation	(148,712		)	(124,213		)
Net fixed assets	$	535,951		$	416,925

Our depreciation expense for the periods presented was as follows:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2012		2011		2012		2011
Depreciation expense	$	9,202	$	5,960	$	27,246	$	17,838

Asset Retirement Obligations

A reconciliation of our liability for asset retirement obligations is as follows:



December 31, 2011	$	5,900
Liabilities incurred and assumed in the current period	5,995
Accretion expense	600
September 30, 2012	$	12,495

We assumed asset retirement obligations of $5.9 million related to pipelines in connection with our acquisition of GOPL. See Note 2 for information related to our acquisitions.