b'KOSMOS ENERGY LTD.Notes to Consolidated Financial Statements (Continued)10. Fair Value Measurements (Continued)Provisional Oil SalesThe value attributable to the provisional oil sales derivative is based on (i) the sales volumes and(ii) the difference in the independent active futures price quotes for the respective index over the termof the pricing period designated in the sales contract and the spot price on the lifting date.Interest Rate DerivativesOur interest rate derivatives consisted of interest rate swaps, whereby the Company paid a fixedrate of interest and the counterparty paid a variable LIBOR-based rate, and capped interest rate swaps,whereby the Company paid a fixed rate of interest if LIBOR is below the cap, and paid the marketrate less the spread between the cap and the fixed rate of interest if LIBOR is above the cap. Thevalues attributable to the Companys interest rate derivative contracts were based on (i) the contractednotional amounts, (ii) LIBOR yield curves provided by independent third parties and corroborated withforward active market-quoted LIBOR yield curves and (iii) a credit-adjusted yield curve as applicableto each counterparty by reference to the CDS market.DebtThe following table presents the carrying values and fair values at December 31, 2018 and 2017:December 31, 2018 December 31, 2017Carrying CarryingValue Fair Value Value Fair Value(In thousands)Senior Notes . . . . . . . . . . . . . . . $ 511,873 $ 525,026 $ 507,600 $ 542,472Corporate Revolver . . . . . . . . . . 325,000 325,000Facility . . . . . . . . . . . . . . . . . . . 1,325,000 1,325,000 800,000 800,000Total . . . . . . . . . . . . . . . . . . . $2,161,873 $2,175,026 $1,307,600 $1,342,472The carrying value of our Senior Notes represents the principal amounts outstanding lessunamortized discounts. The fair value of our Senior Notes is based on quoted market prices, whichresults in a Level 1 fair value measurement. The carrying value of the Facility approximates fair valuesince it is subject to short-term floating interest rates that approximate the rates available to us forthose periods.137'