Oil and natural gas activities (unaudited)

Our oil and natural gas activities are conducted entirely in the United States. Costs incurred in oil and natural gas producing activities are as follows:



	Successor						Predecessor
					Period from		Period from
					March 22, 2017		January 1, 2017
	For the Year Ended December 31,				through		through
	2019		2018		December 31, 2017		March 21, 2017
Property acquisition costs
Proved properties	$	179	$	1,699	$	179	$	527
Unproved properties	22,928		120,610		33,901		2,904
Total acquisition costs	23,107		122,309		34,080		3,431
Development costs	238,664		199,833		140,180		32,657
Exploration costs	8,055		18,876		916		1,241
Total	$	269,826	$	341,018	$	175,176	$	37,329

Depreciation, depletion, and amortization expense of oil and natural gas properties was as follows:



	Successor						Predecessor
					Period from		Period from
					March 22, 2017		January 1, 2017
	For the Year Ended December 31,				through		through
	2019		2018		December 31, 2017		March 21, 2017
DD&A (1)	$	103,732	$	79,070	$	84,899	$	23,442
DD&A per BOE:	$	10.81	$	10.56	$	12.86	$	13.05

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(1)	Includes accretion of asset retirement obligations.

Oil and natural gas properties not subject to amortization consists of unevaluated leasehold acquisition costs, capitalized interest related to the leasehold costs and wells or facilities for which reserve volumes are not classified as proved until completed. The costs of unevaluated oil and natural gas properties, by year incurred, consisted of the following:



	Year Cost Incurred						Total as of
	2019		2018		2017		December 31, 2019
Leasehold acreage (1)	$	5,223	$	70,017	$	258,843	$	334,083
Capitalized interest (2)	7,091		9,694		—		16,785
Wells in progress of completion	20,361		—		—		20,361
Total unevaluated oil and natural gas properties excluded from amortization	$	32,675	$	79,711	$	258,843	$	371,229

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(1)	In the past, the costs associated with unevaluated properties typically related to historical acquisition costs of leasehold acreage. However, the total balance as December 31, 2019 includes an increase in carrying value to fair value of $235,723 as a result of the application of fresh start accounting upon emergence from bankruptcy. See “Note 4: Fresh start accounting.”


(2)	As of December 31, 2019, this amount reflects the cumulative interest capitalized on the historical acquisition cost of leasehold acreage subsequent to our establishing opening balances under fresh start accounting. Interest is not capitalized on amounts related to the fair value gross up discussed above.

The carrying value of wells in progress of completion will be transferred to the amortization base upon completion in 2020. With respect to leasehold acreage, the carrying value of undeveloped leasehold acreage will be evaluated and transferred to the amortization base within the next two to five years. Leasehold acreage also includes value assigned to held-by-production leasehold upon adoption of fresh start accounting; the carrying value of such leasehold will be transferred to the amortization base as those locations are evaluated.