A simple electric impedance sensor embedded in ethanol and regular gasoline blends for determining mass ratios was built and tested in the present work. It was carried out a quantitative evaluation of mixtures for several fuel mass ratios in the temperature range of -10 to 40 degreesC. A non-linear dimensionless electrical conductivity-fuel mass ratio correlation was obtained for a 0-100% ethanol mass content in gasoline. Tests at different temperatures showed that the temperature had an important influence over the mixture bulk conductivity and sensor signal. This work was carried out following the Brazilian automotive industry trend of using ethanol-gasoline mixtures at any proportion to power passenger automobile engines. (C) 2004 Elsevier Ltd. All rights reserved.