The fractional compositions of fatty acid methyl esters from rape and sunflower oils were determined by the method in GOST2177-99. The data obtained can be used to calculate the characteristic temperatures and thermophysical parameters of biofuels. The difference in the boiling points of the esters and their vapors was established. The ingredients of the biofuels and their fractions were determined by gas-liquid chromatography. Fuels of plant origin evaporate in a narrow temperature range so that the fatty acid methyl esters are distributed very unevenly over all fractions. The results obtained can be used to create an adequate mathematical model of evaporation of biofuel in the diesel cylinder.