PROPERTY AND EQUIPMENT

The major categories of property and equipment and related accumulated depletion, depreciation, amortization and impairment as of December 31, 2017 and 2016 are as follows:



	December 31,
	2017			2016
	(In thousands)
Oil and natural gas properties	$	9,169,156		$	6,071,920
Office furniture and fixtures	37,369			21,204
Building	44,565			42,530
Land	4,820			5,252
Total property and equipment	9,255,910			6,140,906
Accumulated depletion, depreciation, amortization and impairment	(4,153,733		)	(3,789,780		)
Property and equipment, net	$	5,102,177		$	2,351,126

No impairment of oil and natural gas properties was required under the ceiling test for the year ended December 31, 2017. At December 31, 2016 and 2015, the net book value of the Company's oil and natural gas properties was above the calculated ceiling as a result of the reduced commodity prices during the years ended December 31, 2016 and 2015, respectively. As a result, the Company recorded an impairment of its oil and natural gas properties under the full cost method of accounting in the amount of $715.5 million and $1.4 billion for the years ended December 31, 2016 and 2015, respectively.

Included in oil and natural gas properties at December 31, 2017 and 2016 is the cumulative capitalization of $165.6 million and $129.9 million, respectively, in general and administrative costs incurred and capitalized to the full cost pool. General and administrative costs capitalized to the full cost pool represent management’s estimate of costs incurred directly related to exploration and development activities such as geological and other administrative costs associated with overseeing the exploration and development activities. All general and administrative costs not directly associated with exploration and development activities were charged to expense as they were incurred. Capitalized general and administrative costs were approximately $35.7 million, $29.3 million and $27.9 million for the years ended December 31, 2017, 2016 and 2015, respectively. The average depletion rate per Mcfe, which is a function of capitalized costs, future development costs and the related underlying reserves in the periods presented, was $0.90, $0.92 and $1.68 per Mcfe for the years ended December 31, 2017, 2016 and 2015, respectively.

The following is a summary of Gulfport’s oil and natural gas properties not subject to amortization as of December 31, 2017:



	Costs Incurred in
	2017		2016			2015			Prior to 2015			Total
	(In thousands)
Acquisition costs	$	1,511,685	$	129,741		$	429,897		$	824,363		$	2,895,686
Exploration costs	—		—			—			—			—
Development costs	5,076		4,607			3,635			2,214			15,532
Capitalized interest	3,871		(536		)	(1,141		)	(438		)	1,756
Total oil and natural gas properties not subject to amortization	$	1,520,632	$	133,812		$	432,391		$	826,139		$	2,912,974

The following table summarizes the Company’s non-producing properties excluded from amortization by area as of December 31, 2017:



	December 31, 2017
	(In thousands)
Utica	$	1,513,452
MidContinent	1,396,642
Niobrara	2,184
Southern Louisiana	552
Bakken	99
Other	45
	$	2,912,974

As of December 31, 2016, approximately $1.6 billion of non-producing leasehold costs was not subject to amortization.

The Company evaluates the costs excluded from its amortization calculation at least annually. Subject to industry conditions and the level of the Company’s activities, the inclusion of most of the above referenced costs into the Company’s amortization calculation typically occurs within three to five years. However, the majority of the Company's non-producing leases in the Utica Shale have five year extension terms which could extend this time frame beyond five years.

A reconciliation of the Company's asset retirement obligation for the years ended December 31, 2017 and 2016 is as follows:



	December 31,
	2017			2016
	(In thousands)
Asset retirement obligation, beginning of period	$	34,276		$	26,437
Liabilities incurred	16,300			10,971
Liabilities settled	(3,057		)	(4,189		)
Accretion expense	1,611			1,057
Revisions in estimated cash flows	25,970			—
Asset retirement obligation as of end of period	75,100			34,276
Less current portion	120			195
Asset retirement obligation, long-term	$	74,980		$	34,081