The viscosities and densities ((293.15 to 353.15) K), speeds of sound ((293.15 to 333.15) K), Surface tensions (room temperature), and flash points were. measured for binary mixtures of n-butylcyclohexane with either toluene or n-hexadecane. Increasing the temperature decreased the densities, and the excess molar volumes of the mixtures were generally positive, suggesting increased spacing due to differences in packing and intermolecular forces. Increasing the temperature also decreased the viscosities, and the McAllister three-body model successfully modeled the viscosity with the larger fitting term corresponding to two molecules of the more viscous substance. The mixture surface tensions and flash points fell between the pure-component values, which ranged from (26.7 to 28.6) mN.m(-1) and (324.7 to 406.2) K, respectively. The speed of sound decreased with increasing mole fraction of n-butylcycylohexane in n-hexadecane, but several speed of sound values for mixtures of n-butylcyclohexane and toluene were lower than those of either component. For both sets of mixtures, the isentropic bulk moduli of several mixtures Were lower than those of their components. These results show that simple blending rules cannot be used to predict the speed of sound and bulk modulus of these mixtures.