The flexibilities observed in Public-Private Partnership (PPP) contracts for road infrastructure projects can also be taken as contractual options. The model developed in the present study had as main focus the establishments of the optimal level of government guarantee to be provided to private initiative in a PPP highway concession, using real option theory integrated with Omega measure, in which had a better response among other proposed VaR and CVaR metrics. Also in an original way, the model contribute to set a minimum revenue guarantees, as part of the european collar option (call and put), integrated to an expansion american call option. The project s present value (PV), considering an option for capacity expansion, was calculated at BRL 2.73 billion, which compared to the expected value of BRL 2.65 billion without flexibility, represents an increase of BRL 73 million to the value of the project in the base case scenario. The present value of the project with the flexibility of expansion (call) and with a minimum revenue guarantee with cap 10 percent of Capex, allows to reach the value of 3.33 for the Omega measure, which is much higher than the previous value of 0.996, obtained only with the european collar option.