This research has three objectives. Our first objective is to apply real options theory, based on Dixit & Pindyck [1994] development to value a listed company. In particular, our intention is to value a company that has investment projects with delay options, in markets subjected to competitors random entry. We adopted the Geometric Brownian Motion to model the market uncertainty. The uncertainty concerning the competitors entry is assumed to be described by a Poisson Process. The company we have chosen is the Companhia Siderúrgica de Tubarão. The main reason behind our choice is the fact that the company has publicly announced that it is studying three big projects for investment.As a second objective, we intend to apply real option theory to value a high technology company using the methodology developed by Schwartz [2000]. In his work, Schwartz valued Amazon.com taking into account of the fact that Amazon`s shareholders have limited liability in case of Amazon`s bankruptcy. Our idea is to adapt Schwartz`s framework to value Globo Cabo, the Organizações Globo subsidiary in the business of cable TV, internet and telecommunications. Our third objective is to study qualitatively how much real options theory can contribute to the business valuation process. Our conclusion will take into account our very limited sample.