The following table provides certain information about the operations of each of our segments:



	2012				2011			2010
	(In thousands)
Revenues:
Contract drilling	$	579,368			$	536,872		$	356,527
Elimination of inter-segment revenue	(49,649		)		(52,221		)	(40,143		)
Contract drilling net of inter-segment revenue	529,719				484,651			316,384
Oil and natural gas	567,944				514,614			399,771
Gas gathering and processing	290,773				284,248			201,320
Elimination of inter-segment revenue	(73,313		)		(76,010		)	(46,804		)
Gas gathering and processing net of inter-segment revenue	217,460				208,238			154,516
Total revenues	$	1,315,123			$	1,207,503		$	870,671
Operating income:
Contract drilling	$	159,188			$	135,085		$	59,601
Oil and natural gas	(77,221		)	⁽³⁾	199,993			175,613
Gas gathering and processing	5,780				17,278			16,985
Total operating income ⁽¹⁾	87,747				352,356			252,199
General and administrative expense	(33,086		)		(30,055		)	(26,152		)
Interest expense, net	(14,137		)		(4,167		)	—
Gain (loss) on derivatives not designated as hedges and hedge ineffectiveness, net	(1,243		)		1,702			1,036
Other income (loss), net	121				(834		)	10,138
Income before income taxes	$	39,402			$	319,002		$	237,221
Identifiable assets:
Contract drilling	$	1,079,736			$	1,118,666		$	998,658
Oil and natural gas	2,214,029				1,820,492			1,441,797
Gas gathering and processing	413,708				247,763			176,596
Total identifiable assets ⁽²⁾	3,707,473				3,186,921			2,617,051
Corporate assets	53,647				69,799			52,189
Total assets	$	3,761,120			$	3,256,720		$	2,669,240
Capital expenditures:
Contract drilling	$	77,520			$	162,208		$	118,806
Oil and natural gas	1,128,349				580,055			463,870
Gas gathering and processing	183,162				79,355			29,815
Other	28,071				10,791			6,417
Total capital expenditures	$	1,417,102			$	832,409		$	618,908
Depreciation, depletion, amortization, and impairment:
Contract drilling	$	81,007			$	79,667		$	69,970
Oil and natural gas:
Depreciation, depletion, and amortization	211,347				183,350			118,793
Impairment of oil and natural gas properties	283,606			⁽³⁾	—			—
Gas gathering and processing	24,388			⁽⁴⁾	16,101			15,385
Other	2,279				1,333			976
Total depreciation, depletion, amortization, and impairment	$	602,627			$	280,451		$	205,124

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(1)	Operating income is total operating revenues less operating expenses, depreciation, depletion, amortization, and impairment and does not include general corporate expenses, gain (loss) on non-designated hedges and hedge ineffectiveness, interest expense, other income (loss), or income taxes.


(2)	Identifiable assets are those used in Unit’s operations in each industry segment. Corporate assets are principally cash and cash equivalents, short-term investments, corporate leasehold improvements, furniture and equipment.


(3)	In June 2012 and December 2012, due to low 12-month average commodity prices, we incurred non-cash ceiling test write downs of our oil and natural gas properties of $115.9 million pre-tax ($72.1 million net of tax) and $167.7 million pre-tax ($104.4 million net of tax), respectively.


(4)	Depreciation, depletion, amortization, and impairment for gas gathering and processing includes a $1.2 million write down of our Erick system.