This study aims to evaluate the economic feasibility of the OPL-70 Project, which involves drilling 100 development wells in Field X within the East Borneo working area under the Production Sharing Contract (PSC) Cost Recovery framework. The study employs a quantitative approach using a Discounted Cash Flow (DCF) model covering the 2025–2033 evaluation period. Key economic indicators, including Net Present Value (NPV), Internal Rate of Return (IRR), Profitability Index (PI), and Discounted Payback Period, are applied to assess the project’s financial viability. Risk and uncertainty are addressed through sensitivity analysis and Monte Carlo simulation to capture the effects of variations in gas production, gas prices, and intangible capital expenditure. The results indicate that the OPL-70 Project generates a positive NPV of USD 18.53 million, an IRR of 13.56% exceeding the company’s hurdle rate, and a PI of 1.05, confirming its economic attractiveness. Probabilistic analysis shows a 96.92% probability of achieving a positive NPV, with limited downside risk. The study concludes that the OPL-70 Project is economically feasible and capable of enhancing gas recovery while extending the economic life of the mature field. The findings provide practical implications for investment decision-making and offer a structured reference for evaluating similar mature gas field developments.