Abstract The relative permittivity of gasoline/methanol blends was determined at 100 kHz, in the full range of composition, at temperatures between 296 K and 323 K. From experimental results, permittivity is fitted to a third degree polynomial on methanol content, and, at each composition, the permittivity of blends decreases linearly with temperature. From the analysis of the experimental data, a model is developed to estimate the relative permittivity as a function of blend composition and temperature. The model fitting is very satisfactory, with an RMS absolute uncertainty of 0.43. The parameters of the model are determined from experimental data for pure gasoline and methanol, and were checked by means of a non-linear fitting using all the experimental data, with very good agreement. Another model is proposed to estimate the composition of blends from temperature and permittivity measurements. From the comparison to experimental data, the RMS absolute uncertainty of the estimation is below 2%.