NOTE 4 - OIL AND NATURAL GAS PROPERTIES

The following table sets forth a summary of oil and natural gas property costs (net of divestitures) at December 31, 2019 and 2018:



	December 31,
	2019			2018
	(In thousands)
Oil and natural gas properties:
Proved	$	478,569		$	358,858
Unproved	109,590			169,863
Total oil and natural gas properties	588,159			528,721
Accumulated depletion, depreciation, amortization and impairment	(359,304		)	(98,342		)
Oil and natural gas properties, net	$	228,855		$	430,379

The following table sets forth a summary of costs withheld from amortization as of December 31, 2019:



	Year of Acquisition
	Total		2019		2018		2017
	(In thousands)
Unamortized costs:
Unproved leasehold costs	$	109,590	$	1,643	$	85,598	$	22,349
Total	$	109,590	$	1,643	$	85,598	$	22,349

For the years ended December 31, 2019 and 2018, $56.2 million and $11.1 million, respectively, of unproved property costs were recorded as impairments of unproved property costs and transferred to proved properties. Impairments for 2019 were the result of title defects, lease expirations, changes to management’s development plans and uncertainty that the Company will have access to necessary funding to either extend the leases expiring in 2020 or begin drilling before their expiration dates. The 2018 impairment of $11.1 million was the result of defective titles for certain leases.

Depreciation, depletion and amortization expense related to proved properties was approximately $32.6 million and $25.2 million, respectively for the years ended December 31, 2019 and 2018. Full-cost ceiling impairments totaling $228.3 million were recorded for the year ended December 31, 2019. For the year ended December 31, 2018, no such impairments were recognized.

The 2019 impairment charges were the result of a decrease in crude oil and natural gas prices used in preparation of the proved reserves estimates. Additionally, proved undeveloped reserves previously included in the Company’s proved reserves report were reclassified as unproved because of the uncertainty regarding the availability of capital for development those reserves as of December 31, 2019. The reclassification of proved undeveloped reserves to unproved are recognized in the Company’s proved reserves report as of December 31, 2019. These changes have contributed, in part, to higher depletion rates for 2019 as compared to 2018.