National Iranian Oil Company (NIOC), one of the largest exploration and production oil companies in the world, faces with numerous investment opportunities. The selection and formation of projects’ basket (portfolio) in this industry needs some considerations on decision makings, key targets, priorities and constraints of NIOC. On the one hand, due to NIOC’s vision as one of the excellent commercial companies of the world in production, refining and export of oil and gas, the necessity of keeping the production level unchanged and enhancing the abilities of production by fields developments and increasing the recovery factor, due to vision, and on the other hand, the numorousity of investment opportunities at different stages of exploration, development, exploitation, production and the complexity of backward and forward linkages of projects and correspondent risks, the number of portfolios is as such as that selecting optimum portfolio and its dynamics through time periods, considering all constraints, are not feasible without applying scientific methods.According to these, a model is presented which identifies the expectations, strategies, targets, priorities and constraints of NIOC, critical success factors (CSFs) and also economic risks of projects, economic evaluation and portfolio management and applies MERAK products (for a few pilot projects at upstream level) in this industry, and determines the optimum basket of the projects. For implementing the system of this model, an organization is required in each planning departments of NIOC. This system as a decision support system (DSS) is able to use the current data, government’s and also the ministry’s strategies, the policies of CEO and other budgetrial constraints and financial considerations, and finally determines the investment priorities and optimum portfolio of NIOC.