Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)This paper presents a model for valuation and decision making, integrating discounted cash flow, real-options pricing and preference theory, aiming to cover the following questions: i) what is the current value of a project?; ii) what is the optimal investment rule?; iii) what is the optimal working interest? The traditional model suggests that, when the project value is above its investment cost, the corporation should invest immediately and incur in 100% working interest. The real option pricing suggests that the corporation should only invest if the project's current value is at least 1.85 times investment cost. The preference theory suggests funding only 44.38% working interest, and partners must acquire the remaining 55.62%. These tools must be integrated in order to allow a more realistic treatment of risk. In general, when the uncertainty (volatility) of cash flow components increases, the two models give more divergent results.O TEXTO COMPLETO DESTE ARTIGO, ESTARÁ DISPONÍVEL À PARTIR DE FEVEREIRO DE 2015.141671323Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)CEPETRO/UNICAMPConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)PETROBRASCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)