Supplementary Information of Oil and Gas Operations—Unaudited | Supplementary Information on Oil and Gas Operations—Unaudited The following tables disclose certain financial data relative to the Company’s oil and gas producing activities, which are located onshore and offshore in the continental United States: Costs Incurred in Oil and Gas Property Acquisition, Exploration and Development Activities ( amounts in thousands ) For the Year-Ended December 31, 2017 2016 2015 Acquisition costs: Proved $ 1,330 $ 3,346 $ 2,287 Unproved (1) 12,762 2,197 2,550 Divestiture of proved leasehold (4,795 ) (7,000 ) — Exploration costs: Proved 9,466 715 29,322 Unproved (287 ) 603 7,677 Development costs 32,622 1,522 9,888 Capitalized general and administrative and interest costs 8,269 7,558 12,881 Total costs incurred $ 59,367 $ 8,941 $ 64,605 For the Year-Ended December 31, 2017 2016 2015 Accumulated depreciation, depletion and amortization (DD&A) Balance, beginning of year $ (1,243,286 ) $ (1,157,455 ) $ (1,648,060 ) Provision for DD&A (31,667 ) (27,962 ) (62,138 ) Ceiling test writedown — (40,304 ) (266,562 ) Sale of proved properties and other (2) (3) (10,707 ) (17,565 ) 819,305 Balance, end of year $ (1,285,660 ) $ (1,243,286 ) $ (1,157,455 ) DD&A per Mcfe $ 1.15 $ 1.19 $ 1.82 (1) During 2017 , the Company acquired approximately 24,600 gross acres for approximately $9.3 million of cash and 2.0 million shares of common stock. (2) During 2015 , the Company sold its Woodford Shale and Mississippian Lime assets for an aggregate cash purchase price of $274.1 million (see Note 2). (3) During 2017 , the Company sold its East Lake Verret assets for net proceeds of approximately $2.2 million and its East Texas saltwater disposal assets for net proceeds of $8.5 million . During 2016 , the Company sold its remaining Oklahoma producing assets for an aggregate purchase price of $17.6 million . During 2015 , the Company sold its Fort Trinidad assets for net proceeds of approximately $0.5 million and its East Haynesville assets for net proceeds of approximately $0.1 million . At December 31, 2017 and 2016 , unevaluated oil and gas properties totaled $21.9 million and $9.0 million , respectively, and were not subject to depletion. Unevaluated costs at December 31, 2017 included $0.7 million related to two facilities in progress at year-end. At December 31, 2016 , unevaluated costs included $0.4 million related to one development well in progress at year-end, which were transferred to evaluated oil and gas properties during 2017 . The Company capitalized $1.6 million , $0.9 million and $4.7 million of interest during 2017 , 2016 and 2015 , respectively. Of the total unevaluated oil and gas property costs of $21.9 million at December 31, 2017 , $14.6 million , or 67% , was incurred in 2017 , $2.0 million , or 9% , was incurred in 2016 and $5.2 million , or 24% , was incurred in prior years. In connection with the sale of the Company's Gulf of Mexico assets, approximately $5.5 million , or 25% of the total unevaluated balance at December 31, 2017 , was transferred to evaluated oil and gas properties in 2018. Of the remaining unevaluated balance at December 31, 2017 , the Company expects the majority of the costs will be evaluated within the next three years, including $4.1 million expected to be evaluated during 2018 . Oil and Gas Reserve Information The Company’s net proved oil and gas reserves at December 31, 2017 have been estimated by independent petroleum engineers in accordance with guidelines established by the SEC using a historical 12-month, first of month, average pricing assumption. The estimates of proved oil and gas reserves constitute those quantities of oil, gas,and natural gas liquids, which, by analysis of geoscience and engineering data, can be estimated with reasonable certainty to be economically producible—from a given date forward, from known reservoirs, and under existing economic conditions, operating methods, and government regulations—prior to the time at which contracts providing the right to operate expire, unless evidence indicates that renewal is reasonably certain, regardless of whether deterministic or probabilistic methods are used for the estimation. However, there are numerous uncertainties inherent in estimating quantities of proved reserves and in providing the future rates of production and timing of development expenditures. The following reserve data represents estimates only and should not be construed as being exact. In addition, the present values should not be construed as the current market value of the Company’s oil and gas properties or the cost that would be incurred to obtain equivalent reserves. The following table sets forth an analysis of the Company’s estimated quantities of net proved and proved developed oil (including condensate), gas and natural gas liquid reserves, all located onshore and offshore in the continental United States: Oil NGL Natural Gas Total Proved reserves as of December 31, 2014 2,437 73,498 309,025 397,148 Revisions of previous estimates (211 ) (3,571 ) (9,852 ) (14,698 ) Extensions, discoveries and other additions 163 16,078 45,645 62,702 Sale of reserves in place (54 ) (45,692 ) (186,972 ) (232,988 ) Production (529 ) (5,487 ) (25,502 ) (34,160 ) Proved reserves as of December 31, 2015 1,806 34,826 132,344 178,004 Revisions of previous estimates 247 (4,380 ) (11,854 ) (14,748 ) Extensions, discoveries and other additions — — 1,485 1,485 Sale of reserves in place (154 ) — (24,834 ) (25,759 ) Production (502 ) (3,871 ) (16,617 ) (23,501 ) Proved reserves as of December 31, 2016 1,397 26,575 80,524 115,481 Revisions of previous estimates 308 (7,269 ) 381 (5,040 ) Extensions, discoveries and other additions 777 4,565 64,704 73,931 Purchase of producing properties 48 — 473 761 Sale of reserves in place (90 ) — (1,033 ) (1,573 ) Production (592 ) (4,450 ) (19,611 ) (27,613 ) Proved reserves as of December 31, 2017 1,848 19,421 125,438 155,947 Proved developed reserves As of December 31, 2015 1,549 15,792 78,533 103,615 As of December 31, 2016 1,212 13,073 47,349 67,694 As of December 31, 2017 1,078 12,564 57,409 76,441 Proved undeveloped reserves As of December 31, 2015 257 19,034 53,811 74,389 As of December 31, 2016 185 13,502 33,175 47,787 As of December 31, 2017 770 6,857 68,029 79,506 Year Ended December 31, 2017 During 2017 , the Company’s estimated proved reserves increase d by 35% . The increase in reserves was the result of 73.9 Bcfe added due to the Company's drilling program in East Texas where it drilled eight gross wells during 2017 . In response to low ethane prices, during 2017 the Company elected to bypass ethane processing on a portion of its East Texas production. As a result, the Company reduced its estimated proved ngl reserves to reflect the assumption that ethane would continue to not be recovered as natural gas liquids. Overall, the Company had a 100% drilling success rate during 2017 . Year Ended December 31, 2016 During 2016 , the Company’s estimated proved reserves decrease d by 35% primarily due to the divestiture of the Company's remaining Oklahoma assets and significant reductions in capital spending during 2016 . Extensions, discoveries and other additions of 1.5 Bcfe were primarily due to the successful completion of the Company's final Oklahoma wells. Revisions of previous estimates included the reclassification of certain PUD reserves to probable reserves as a result of the Company's assessment of the timing of development. Overall, the Company had a 100% drilling success rate during 2016 on 5 gross wells drilled. Year Ended December 31, 2015 During 2015 , the Company's estimated proved reserves decrease d by 55% primarily due to the divestiture of the majority of the Company's Woodford Shale and Mississippian Lime assets. Extensions, discoveries and other additions of 63 Bcfe were primarily due to successful drilling programs in the Company's Oklahoma and East Texas fields. The Company added approximately 17 Bcfe of proved reserves in Oklahoma and 44 Bcfe in Texas. Overall, the Company had a 95% drilling success rate during 2015 on 56 gross wells drilled. The following tables (amounts in thousands) present the standardized measure of future net cash flows related to proved oil and gas reserves together with changes therein, as defined by ASC Topic 932. Future production and development costs are based on current costs with no escalations. Estimated future cash flows have been discounted to their present values based on a 10% annual discount rate. Standardized Measure December 31, 2017 2016 2015 Future cash flows $ 539,244 $ 299,035 $ 487,834 Future production costs (184,171 ) (117,283 ) (171,678 ) Future development costs (128,447 ) (83,720 ) (116,591 ) Future income taxes — — — Future net cash flows 226,626 98,032 199,565 10% annual discount (99,329 ) (30,763 ) (71,880 ) Standardized measure of discounted future net cash flows $ 127,297 $ 67,269 $ 127,685 Changes in Standardized Measure Year Ended December 31, 2017 2016 2015 Standardized measure at beginning of year $ 67,269 $ 127,685 $ 548,562 Sales and transfers of oil and gas produced, net of production costs (70,362 ) (35,993 ) (55,849 ) Changes in price, net of future production costs 53,516 (30,427 ) (267,710 ) Extensions and discoveries, net of future production and development costs 50,977 864 70,928 Changes in estimated future development costs, net of development costs incurred during this period 17,144 26,356 31,007 Revisions of quantity estimates (7,482 ) (14,889 ) (14,427 ) Accretion of discount 6,727 12,769 60,071 Net change in income taxes — — 52,149 Purchase of reserves in place 549 — — Sale of reserves in place (1,305 ) (16,701 ) (194,454 ) Changes in production rates (timing) and other 10,264 (2,395 ) (102,592 ) Net increase (decrease) in standardized measure 60,028 (60,416 ) (420,877 ) Standardized measure at end of year $ 127,297 $ 67,269 $ 127,685 The historical twelve-month, first day of the month, average prices of oil, gas and natural gas liquids used in determining standardized measure were: 2017 2016 2015 Oil, $/Bbl $52.49 $40.85 $50.29 Ngls, $/Mcfe 3.23 2.40 2.24 Natural Gas, $/Mcf 3.03 1.82 2.41 |