up to 55% of total production prior to profit oil being split between the government of Mauritania and the contractor. Profit oil is then apportioned based upon ‘‘R-factor’’ tranches, where the R-factor is cumulative net revenues divided by the cumulative investment. At the election of the government of Mauritania, the government may receive its share of production in cash or in kind. A corporate tax rate of 27% is applied to profits at the license level. The terms of exploration periods of these Offshore Blocks are all ten years and include an initial exploration period of four years followed by the first extension period of three years and the second extension period of three years. Kosmos is currently in the first extension period of the blocks, expiring in June 2019. In the event of commercial success, we have the right to develop and produce oil for 25 years and gas for 30 years from the grant of an exploitation authorization from the government, which may be extended for an additional period of 10 years under certain circumstances. In September 2017, we acquired a 15% non-operated participating interest in Block C18 offshore Mauritania. Based on the terms of the agreement, we will reimburse a portion of past and interim period costs and partially carry Tullow’s share of a planned 3D seismic program. We will also pay Tullow $2.5 million by the end of the initial phase of the exploration period for additional carry of seismic and other joint account costs. SMHPM currently has a 10% carried participating interest during the exploration period. Should a commercial discovery be made, SMHPM’s 10% carried interest is extinguished and SMHPM will have an option to acquire a participating interest between 10% and 15%. SMHPM will pay its portion of development and production costs in a commercial development. The terms of exploration periods are ten years and include an initial exploration period of seven years from the effective date (June 15, 2012), including extensions received prior to our entry into Block 18. The first exploration phase includes a 7,600 square kilometer 3D seismic requirement, which is currently being acquired. Senegal Exploration Agreements In June 2015, we entered the first renewal of the exploration period for the Senegal Blocks Contract Areas, which lasts for three years. The exploration phase of each contract area may be extended to December 2020 at our election subject to our fulfilling specific work obligations including an exploration well in the final period of two and one half years. In the event of commercial success, we have the right to develop and produce oil and/or gas for a period of 25 years from the grant of an exploitation authorization from the government, which may be extended for at least one additional period of 10 years under certain circumstances. Sao Tome and Principe Exploration Agreements In late 2015 and early 2016, Kosmos entered into petroleum contracts for Blocks 5, 6, 11 and 12 in Sao Tome and Principe. In Block 11, the Agencia Nacional Do Petroleo De Sao Tome E Pr´ ıncipe (‘‘ANP STP’’) has a carried 15% participating interest. The production sharing contract was awarded in July 2014, and provides for an initial exploration period of eight years with possible extensions and includes a first phase exploration period of four years followed by the second phase of two years and the third phase of two years. The block is currently in the first phase, expiring in July 2019 after receiving a one year extension in November 2017. The next exploration phases are subject to fulfillment of specific work obligations. In the event of commercial success, we have the right to develop and produce oil and/or gas for a period of 20 years from the approval of a field development program by ANP STP, which may be extended for additional periods of five years until all commercial hydrocarbons have been depleted. 35