5. Fixed Assets and Asset Retirement Obligations

Fixed Assets

Fixed assets consisted of the following:


	March 31, 2012			December 31, 2011
Land, buildings and improvements	$	13,207		$	13,140
Pipelines and related assets		196,790			167,865
Machinery and equipment		47,342			46,233
Transportation equipment		20,902			21,732
Marine vessels		293,106			262,216
Office equipment, furniture and fixtures		4,072			3,778
Construction in progress		30,144			14,236
Other		12,048			11,938

Fixed assets, at cost		617,611			541,138
Accumulated depreciation		(131,928	)		(124,213	)

Net fixed assets	$	485,683		$	416,925

Depreciation expense was $8.8 million and $5.8 million for the three months ended March 31, 2012 and 2011, respectively.

Asset Retirement Obligations

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


Asset retirement obligations as of December 31, 2011	$	5,900
Liabilities incurred and assumed in the current period		5,995
Accretion expense		200

Asset retirement obligations as of March 31, 2012	$	12,095

During the three months ended March 31, 2012, we assumed asset retirement obligations of $5.9 million related to pipelines in connection with our acquisition of GOPL. See Note 3 for information related to our acquisitions.