In the present work, samples of Brazilian gasoline type C previously mixed with hydrated ethanol at concentrations of 20, 40, 60 and 80 vol.% were analyzed by distillation, octane number, specific mass, pH and conductivity, in order to evaluate the physico-chemical properties for a better comprehension of the effects caused by the flex-fuel technology. The obtained results were compared with the specifications of the ANP Agencia Nacional de Petroleo, Gas Natural e Biocombustiveis - that is the federal regulatory agency for monitoring of the quality of fuels in Brazil. It was observed that there exists an ideal concentration of hydrated ethanol for addition in gasoline type C in order to obtain good properties for application in the flex-fuel technology. (C) 2006 Elsevier B.V. All rights reserved.