b'KOSMOS ENERGY LTD.Notes to Consolidated Financial Statements (Continued)11. Asset Retirement ObligationsThe following table summarizes the changes in the Companys asset retirement obligations:December 31,2018 2017(In thousands)Asset retirement obligations:Beginning asset retirement obligations . . . . . . . . . . . . . . . . . $ 66,595 $63,574Additions associated with the acquisition of DGE . . . . . . . . . 74,482 Liabilities incurred during period . . . . . . . . . . . . . . . . . . . . . 5,311 Liabilities settled during period . . . . . . . . . . . . . . . . . . . . . . (3,345) Revisions in estimated retirement obligations . . . . . . . . . . . .(3,945)Accretion expense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8,910 6,966Ending asset retirement obligations . . . . . . . . . . . . . . . . . . . $151,953 $66,595The asset retirement obligations reflect the estimated present value of the amount ofdismantlement, removal, site reclamation, and similar activities associated with our oil and gasproperties. The Company utilizes current cost experience to estimate the expected cash outflows forretirement obligations. The Company estimates the ultimate productive life of the properties, arisk-adjusted discount rate, and an inflation factor in order to determine the current present value ofthis obligation. To the extent future revisions to these assumptions impact the present value of theexisting asset retirement obligation, a corresponding adjustment is made to the oil and gas propertybalance.12. Equity-based CompensationRestricted Stock Awards and Restricted Stock UnitsOur Long-Term Incentive Plan (LTIP) provides for the granting of incentive awards in the formof stock options, stock appreciation rights, restricted stock awards, restricted stock units, among otheraward types. In January 2018 and January 2015, the board of directors approved amendments to theplan which added 11.0 million and 15.0 million shares, respectively, to the plan which were approved atthe corresponding Annual General Meeting. The LTIP as amended provides for the issuance of50.5 million shares pursuant to awards under the plan. As of December 31, 2018, the Company hadapproximately 15.2 million shares that remain available for issuance under the LTIP.We record equity-based compensation expense equal to the fair value of share-based paymentsover the vesting periods of the LTIP awards. We recorded compensation expense from awards grantedunder our LTIP of $35.2 million, $40.0 million and $40.1 million during the years ended December 31,2018, 2017 and 2016, respectively. The total tax benefit for the years ended December 31, 2018, 2017and 2016 was $6.6 million, $13.2 million and $13.0 million, respectively. Additionally, we expensed a nettax shortfall (windfall) related to equity-based compensation of $(0.4) million, $3.1 million and$5.5 million for the years ended December 31, 2018, 2017 and 2016, respectively. The fair value ofawards vested during 2018, 2017 and 2016 was approximately $85.1 million, $21.2 million, and$14.4 million, respectively. The Company granted both restricted stock awards and restricted stock unitswith service vesting criteria and granted both restricted stock awards and restricted stock units with acombination of market and service vesting criteria under the LTIP. Substantially, all of these awards138'