The high speed rail between Rio de Janeiro and Campinas will be auctioned in 2010 as a concession for a 40 year period. The project has an estimated total investment of R$34.6bi, of which R$7bi consists of private equity. However, being a greenfield railway, the project presents high uncertainty regarding future traffic, possibly compromising its economic feasibility and discouraging the private sector’s participation. Although the NPV of the project for the stakeholder is a positive R$49mi, it is estimated that there is a 50.8% probability of it being negative, which represents a significant risk for the private investor. One way to increase the project’s attractiveness is through minimum revenue government guarantees, where a demand floor for each year is established according to a percentage of projected demand within the legal framework of a Public-Private Partnership (PPP). This dissertation applies Real Options Theory to value the project assuming such government guarantee. It is shown that a 60% guarantee reduces the risk of investor loss from 50.8% to 33.2%, contributing to the economic and financial feasibility of the project. Furthermore, increasing levels of guarantees have a higher impact on risk and also imply higher costs for the government.