Mixtures of n-dodecane with C10H14 aromatic isomers (isobutylbenzene, sec-butylbenzene, tert-butylbenzene, and 1,3-diethylbenzene) were analyzed for density, viscosity, speed of sound, surface tension, and flash point. As the concentration of the aromatic component increased, densities, bulk moduli, and surface tensions increased, and viscosities and flash points decreased. Concentration increases caused the speed of sound of 1,3-diethylbenzene to increase monotonically, but for the other compounds, the speed of sound initially decreased before increasing to their maximum value. Excess molar volumes, V-m(E), and excess isentropic compressibilities were positive, and excess speeds of sound, c(E), were negative, indicating non-ideal behavior. Viscosity deviations were negative for all mixtures, and excess molar Gibbs energies of activation for viscous flow did not differ statistically from zero. Mixtures of 1,3-diethylbenzene deviated from ideal mixture behavior the least, and tert-butylbenzene deviated from ideal mixture behavior the most. These mixtures alone would not be good surrogate mixtures for diesel and jet fuel because no mole fraction matched both viscosity and density. The addition of other compounds could remedy this problem.