b'qualifications and exceptions. Certain of these covenants will be terminated if the Senior Notes areassigned an investment grade rating by both Standard & Poors Rating Services and Fitch Ratings Inc.and no default or event of default has occurred and is continuing.Collateral. The Senior Notes are secured (subject to certain exceptions and permitted liens) by afirst ranking fixed equitable charge on all currently outstanding shares, additional shares, dividends orother distributions paid in respect of such shares or any other property derived from such shares, ineach case held by us in relation to our wholly-owned subsidiary, Kosmos Energy Holdings, pursuant tothe terms of the Charge over Shares of Kosmos Energy Holdings dated as of December 20, 2018,among Kosmos Energy Delaware Holdings, LLC, Credit Agricole Corporate and Investment Bank, asSecurity and Intercreditor Agent, and Wilmington Trust, National Association, as Trustee to the SeniorNotes. The Senior Notes share pari passu in the benefit of such equitable charge based on therespective amounts of the obligations under the Indenture and the amount of obligations under theCorporate Revolver. The Guarantees are not secured.Contractual ObligationsThe following table summarizes by period the payments due for our estimated contractualobligations as of December 31, 2018:Payments Due By Year(4)Total 2019 2020 2021 2022 2023 ThereafterPrincipal debt repayments(1) . . . $2,175,000 $$$685,600 $614,100 $305,100 $570,200Interest payments on long-termdebt(2) . . . . . . . . . . . . . . . . . 593,217 147,936 145,347 137,715 73,236 47,528 41,455Operating leases(3) . . . . . . . . . . 36,508 2,775 4,173 3,276 3,326 3,376 19,582(1) Includes the scheduled principal maturities for the $525.0 million aggregate principal amount ofSenior Notes issued in August 2014 and April 2015, borrowings under the Facility and theCorporate Revolver. The scheduled maturities of debt related to the Facility are based on, as ofDecember 31, 2018, our level of borrowings and our estimated future available borrowing basecommitment levels in future periods. Any increases or decreases in the level of borrowings orincreases or decreases in the available borrowing base would impact the scheduled maturities ofdebt during the next five years and thereafter.(2) Based on outstanding borrowings as noted in (1) above and the LIBOR yield curves at thereporting date and commitment fees related to the Facility and Corporate Revolver and interest onthe Senior Notes.(3) Primarily relates to corporate office and foreign office leases.(4) Does not include purchase commitments for jointly owned fields and facilities where we are notthe operator and excludes commitments for exploration activities, including well commitments andseismic obligations, in our petroleum contracts. The Companys liabilities for asset retirementobligations associated with the dismantlement, abandonment and restoration costs of oil and gasproperties are not included. See Note 11 of Notes to the Consolidated Financial Statementsincluded in Item 8. Financial Statements and Supplementary Data for additional informationregarding these liabilities.We currently have a commitment to drill one exploration well in Mauritania and Namibia and twoexploration wells in Senegal. Our partner is obligated to fund our share of the cost of the explorationwells, subject to the remaining exploration and appraisal carry covering both our Mauritania andSenegal blocks. In Sao Tome and Principe, we have a 3D seismic requirement of approximately 13,500square kilometers.95'