Until 1997 The Brazilian Electric Sector was basically a monopoly administrated by federal and state enterprises. In the second semester of 1997 it was begun privatizations and the restructuring process. Before Brazilian Electric Sector restructuring process, the planning of generation expansion was made through a centralized program which focus in minimize the investment and operation costs. The generation expansion was a decision variable of the problem. However, one of the assumptions of the restructuring sector process was and continues to be the private agent realization of a big share of the new investment in generation. So, the generation expansion is not more centralized, becoming a variable, which depends of the investment affordability of this agent. In this context, the present thesis studies the private investment dynamics in thermoelectric generation using Real Options. The dynamic of investment in thermal Plants will be studied in three different situations: In the first, it will be used a model of real options / decision analysis to determine the best timing of construction, considering that exists an exogenous uncertainty in the thermal supply expansion. In the second situation, the same model will be used to define the best timing of investment in thermal plants, considering that exists demand uncertainty, and that the supply expansion remains constant. In the third situation, the supply expansion occurs in response of the demand uncertainty evolution and the strategic interactions between the agents. It will be used a real options/ decision analysis/ game theory model. The main results obtained were the threshold contracted prices and the determination of the best time to invest as a function of some problem variables. It was possible to compare the different studied situations, showing that the competition could delay investments.