The flex fuel car technology was developed by the Bosch Research Center in Brazil, and the firs model was launched in the market in 2003. The concept of flex fuel automobile derived from the possibility of using ethanol, gas or any proportion of this mixture in a fuel tank. The fuel flexibility and its price volatility add value to the vehicle because the consumer has the option to choose the cheapest fuel each time he needs it. We perform the valuation of the flex fuel automobile using Real Options Approach to Dynamic Cash Flow Simulation. The results show that the value of the flex fuel option is significant and can represent from 5% to 10% of the price of the automobile. We also compare this method to the quadrinomial decision tree model and show that while both provide similar results, the simulation method is similar and less computationally intensive.