Offshore South East Sumatra Block is an active oil and gas block in Indonesia operated by PT. Pertamina Upstream Energy Offshore South East Sumatra (PT. PHE OSES). The research framework of the economic valuation is started with evaluating the business environment for PT. PHE OSES based on external situation and internal organization analysis (PESTEL, Porter Five forces and SWOT) to identify the dynamic situation and the potential consequences to the organization. The business environment analysis will be followed by economic valuation and sensitivity analysis to available investment opportunity using capital budgeting framework which are simulated during the economic life of prospect field under the gross split scheme. Business strategy that was initially designed by considering the external business environment and internal situation of the organization is expected to ensure the organization to sustain the competitive advantage and heading the right direction otherwise business decision that was made without understanding the business environment change could risk the organization to invest in non-sustainable business opportunity. Future discussion with the stakeholders in energy business might be required to provide insights on methods to stimulate the oil and gas business without jeopardizing the State interest. Oil production control and efficiency of Capital Expenditure and being two most influential factor in the viability study of investment in the Triple-Has prospect, thus it is highly recommended to be the focus of PT. PHE OSES to expand the economic value of Triple-Has prospect.