In January of 2002 the fuel sector entered definitively the free market. Fuel prices from refineries stopped being regulated and importation of derivatives of oil by private companies was allowed. Ethanol prices had been freed since the end of the 1990’s. The aims of this study are: to characterize the functioning of the fuel market identifying the main factors that interfere on decision-taking of its agents; to estimate equations of demand for gasoline C, supply of anhydrous ethanol and gasoline and to figure the elasticities of transmission of prices. Results have shown inelasticity in relation to the income and to the price of the demand for gasoline and inelasticity-price for the supply of anhydrous ethanol and gasoline A. Considering the transmission elasticities, it was concluded that an increase in the demand for gasoline C tends to increase the price of anhydrous ethanol more than proportionally to the price of gasoline C; the price of the anhydrous ethanol will tend to vary more than proportionally to the price of gasoline C in case of shocks of supply of anhydrous ethanol and, in the case of variations in the supply of gasoline A, the prices of the anhydrous ethanol and of gasoline C tend to vary in opposing directions.