A government must be committed to the continuous improvement of its public services and a significant part of this commitment involves ensuring that public funds are spent on activities and projects that provide the greatest benefits to society. Conducting a Cost-Benefit Analysis (CBA) provides the decision maker with quantitative comparisons of investment alternatives, together with additional supporting information about all costs and benefits that could not be quantified, assisting in decision making. A limitation of CBA is that despite uncertainty being an inherent aspect to it, the future flows of costs and benefits are estimated based only on information and assumptions available at the time of the investment decision. Since there already is extensive literature demonstrating the increasing importance of flexible business management, with constant revisions of previously designed strategies and plans, one realizes the need for a tool like Real Options Analysis (ROA) that allows the inclusion of uncertainty and managerial flexibility in CBA. The main objective of this thesis was to develop a theoretical framework for the socioeconomic evaluation of projects under uncertainty through the combination of cost-benefit analysis and real options analysis. In addition, it also tried to verify if the proposed framework produces satisfactory results when applied in practice. The integrated approach was called COst-Benefit Real options Analysis (COBRA). In order to verify if this new approach adds value to a project, it was applied in the evaluation of a biomass powerplant with an ethanol production unit in a scenario without flexibility (Base Case) and with flexibility (Flexible Case). Through this application, it was found that the project evaluation through the COBRA approach increased its value by 93 million, turned the project into something beneficial for society, enabled government subsidies and made de project feasible. The results indicate that, if applied correctly, this approach may prove to be a viable alternative to the problem of socioeconomic evaluation of projects with flexibilities under uncertainty.