Nowadays, world´s economic issues are characterized by dynamism and strong uncertainties, especially in questions related to future decisions. As a consequence of this, the theory of investment analysis has been changing a lot. More and more it has been observed a growing necessity to include the concept of managerial flexibility in project valuation. Plenty of authors criticize the currently used investment analysis method, mainly represented by the discounted cash flow. Besides, several researches have been carried out to analyze the advantages of using the Real Options theory, which is characterized exactly by including this managerial flexibility, so important to the investment and project studies. Managerial flexibility is important exactly because it is capable to guarantee strategic adaptability to the decision makers. Among the projects that need most this new valuation criterion, it is important to mention those related to petroleum investments, due to its complexity and to the fact that petroleum projects demand voluminous sums of investment, requiring therefore, a more detailed and careful analysis. Dias (2005), in his studies about Real Option theory in petroleum area, has developed two analysis models: Business and Rigid Cash Flow. The main proposal of this dissertation is to compare these two models and to draw some conclusions about the best investment decision, regarding not only the best moment to invest - timing decisions - but also the valuation projects issues. To make this comparative analysis, some graphs have been developed in Excel. The data used to construct such graphs were generated by a VBA (Visual Basic for Applications) program, also developed by Dias (2005).