b'with a first exploration period expiring in March 2023. The first exploration period consists of twosub-periods of three and two years, respectively. The first exploration sub-period work programincluded an approximately 6,000 square kilometer 3D seismic acquisition requirement across the blocks,which was completed in November 2018.In June 2018, we closed a farm-in agreement with a subsidiary of Ophir Energy plc (Ophir) forBlock EG-24, offshore Equatorial Guinea, whereby we acquired a 40% non-operated participatinginterest. As part of the agreement, we reimbursed a portion of Ophirs previously incurred explorationcosts and will fully carry Ophirs share of the costs of a planned 3D seismic program as well as pay adisproportionate share of the well commitment should we enter the second exploration sub-period. Thepetroleum contract covers approximately 3,500 square kilometers, with a first exploration period ofthree years from the effective date (March 2018) which can be extended up to four additional years atour election subject to fulfilling specific work obligations. The first exploration period work programincludes a 3,000 square kilometer 3D seismic acquisition requirement, which was completed inNovember 2018. In January 2019, we entered into an agreement to acquire Ophirs remaining interestin and operatorship of the block, subject to customary governmental approvals, which will result inKosmos owning an 80% interest in Block EG-24. Should a commercial discovery be made, GEPetrols20% carried interest will convert to a 20% participating interest for all development and productionoperations.In November 2018, we completed a 3D seismic survey of approximately 9,500 square kilometersover blocks EG-21, EG-24, S and W offshore Equatorial Guinea, and approximately 200 squarekilometers over Block G. The seismic data will be processed with the objective of high gradingprospects for drilling in 2019.Ceiba Field and Okume ComplexEquity Method InvestmentIn the fourth quarter of 2017, through a joint venture with an affiliate of Trident, we acquired allof the equity interest of Hess International Petroleum Inc., a subsidiary of Hess Corporation (Hess),which holds an 85% paying interest (80.75% revenue interest) in the Ceiba Field and Okume Complexassets. Under the terms of the agreement, Kosmos and Trident each own 50% of Hess InternationalPetroleum Inc. Hess International Petroleum Inc. was subsequently renamed Kosmos-TridentInternational Petroleum Inc. (KTIPI). Kosmos is primarily responsible for exploration and subsurfaceevaluation while Trident is primarily responsible for production operations and optimization. Thetransaction expands our position in the Gulf of Guinea and provides immediate cash flow throughexisting production with potential to increase existing production through exploration opportunities withpotential low cost tie-backs through the existing infrastructure. The gross acquisition price was$650 million effective as of January 1, 2017. After post closing entries Kosmos paid net cash ofapproximately $231 million. The transaction was accounted for as an equity method investment. Oilproduction from the Ceiba Field and Okume Complex averaged approximately 44,000 barrels gross(28,000 barrels net) of oil per day during 2018.Effective as of January 1, 2019, our outstanding shares in KTIPI were transferred to Trident inexchange for a 40.375% undivided interest in the Ceiba Field and Okume Complex. As a result, ourinterest in the Ceiba Field and Okume Complex will be accounted for under the proportionateconsolidation method of accounting going forward.In May 2018, we signed a farm-out agreement with a subsidiary of Trident covering blocks S, Wand EG-21 offshore Equatorial Guinea. Under the terms of the agreement, Trident acquired a 40%non-operated participating interest in the blocks and Kosmos remains the operator. In August 2018, wecompleted the farm-out agreement covering blocks S, W and EG-21 offshore Equatorial Guinearesulting in a $7.7 million gain.21'