The present invention relates to a fuel identification system and method normally applied to internal combustion engine vehicles of the flex-fuel type by means of which it is possible to identify the composition of the fuel used at each point in time, particularly the ratio used in a gasoline/ethanol blend or detect the presence of air or fuel in the vapor state in the fuel line, using the same device that heats the fuel. The system according to the invention comprises a heating resistor (3) having a variable resistance value as a function of its temperature, said resistor being arranged in contact with the fuel (2); a current measuring device (6), which measures the current through the variable resistor (3); and an electronic control unit (4) connected to the resistor (3) and connected to the current measuring device (6), receiving from it the measured resistor (3) current values, the electronic control unit (4) comprising data processing means to help identify fuel (2) properties based on the current in resistor (3).