The transesterification of sunflower seed oil was carried out in supercritical ethanol without using any catalyst. Ethyl esters of vegetable oils have several outstanding advantages because ethanol is derived from agricultural products and is renewable and biologically less objectionable in the environment. On the other hand, because of lower volatility, ignition delay and combustion problems could occur when ethyl esters are used. In the present work, ethanol is added to enhance the vapor pressure of biodiesel. The bubble-point pressures of mixtures of biodiesel and ethanol as a function of temperature were measured by comparative ebulliometry with inclined ebulliometers. Experimental data of vapor pressures and equilibrium temperatures were correlated by the Antoine equation. The bubble-point lines of pressure versus the composition at different temperatures and the temperature versus the composition at different pressures were obtained. It is found that the mixtures of biodiesel and ethanol have visible positive deviations from Raoult's law. The addition of ethanol has a critical effect on the vapor pressure of fuels.