During the years ended December 31, 2019 and 2018, additions to oil and natural gas properties of $0.1 million and $0.3 million, respectively, were recorded for estimated costs of future abandonment related to new wells drilled or acquired. During the years ended December 31, 2019 and 2018, the Company had no capitalized exploratory well costs, nor costs related to share-based compensation, general corporate overhead or similar activities. Users of this information should be aware that the process of estimating quantities of “proved” and “proved developed” oil and natural gas reserves is very complex, requiring significant subjective decisions in the evaluation of all available geological, engineering and economic data for each reservoir. The data for a given reservoir may also change substantially over time as a result of numerous factors including, but not limited to, additional development activity, evolving production history and continual reassessment of the viability of production under varying economic conditions. As a result, revisions to existing reserve estimates may occur from time to time. Although every reasonable effort is made to ensure reserve estimates reported represent the most accurate assessments possible, the subjective decisions and variances in available data for various reservoirs make these estimates generally less precise than other estimates included in the financial statement disclosures. Proved reserves represent estimated quantities of oil, natural gas and natural gas liquids that geological and engineering data demonstrate, with reasonable certainty, to be recoverable in future years from known reservoirs under economic and operating conditions in effect when the estimates were made. Proved developed reserves represent estimated quantities expected to be recovered through wells and equipment in place and under operating methods used when the estimates were made. 28 Oil and Natural Gas Reserves Capitalized Costs Years Ended December 31, 2019 2018 Acquisition cost $^{(1)}$: Proved $ (141) $ 41,569 Unproved (125 ) 31,268 Exploration costs: Abandonment costs 653 — Geological and geophysical — 630 Development costs 210,520 153,161 Total additions $ 210,907 $ 226,628 December 31, 2019 2018 Oil and gas properties, successful efforts method: Proved properties $ 1,046,208 $ 830,843 Accumulated impairment to proved properties (75,400 ) (75,400 ) Proved properties, net of accumulated impairments 970,808 755,443 Unproved properties 305,961 311,828 Accumulated impairment to Unproved properties (45,690) (45,688) Unproved properties, net of accumulated impairments 260,271 266,140 Land 5,382 5,382 Total oil and gas properties, net of accumulated impairments 1,236,461 1,026,965 Accumulated depreciation, depletion and amortization (195,567) (127,256) Net oil and gas properties $ 1,040,894 $ 899,709 Capitalized costs, impairment, and depreciation, depletion and amortization relating to the Company’s oil and natural gas properties producing activities, all of which are conducted within the continental United States as of December 31, 2019 and 2018, are summarized below ( in thousands ): (1) Acquisition costs incurred during 2019 consisted primarily of purchase price adjustments related to 2018 acquisitions and during 2018 consisted primarily of an acreage trade in the Midland Basin.