This work reports physical property measurements of binary mixtures of n-hexylbenzene (1) and n-butylbenzene (1) in 2,2,4,6,6-pentamethylheptane (2) and 2,2,4,4,6,8,8-heptamethylnonane (2) at temperatures within the range 253.15-333.15 K. Mixture densities, speeds of sound, and calculated bulk moduli increased with increasing aromatic compound concentration. Excess molar volumes were positive for 2,2,4,4,6,8,8-heptamethylnonane mixtures, negative for hexylbenzene/2,2,4,6,6-pentamethylheptane mixtures, and close to zero for butylbenzene/2,2,4,6,6-pentamethylheptane mixtures at 293.15 K. Excess speeds of sound were positive for all mixtures at 298.15 K, except for n-butylbenzene/,2,2,4,4,6,8,8-heptamethylnonane mixtures, which were close to zero. These results show that compressibility as well as volume change is important for excess speeds of sound. Kinematic viscosities decreased as the aromatic concentration increased at 293.15 K, except for hexylbenzene (x(1)) in 2,2,4,6,6-pentamethylheptane, where increasing hexylbenzene caused a slight viscosity decline before increasing to the value for hexylbenzene. Viscosities were successfully modeled using the McAllister equation. The excess molar Gibbs energy of activation for viscous flow at 293.15 K was not statistically different from zero, which suggests ideal behavior for viscosity. Mixture surface tensions at room temperature and flash points fell within the values of the pure components. Many of these mixtures have property values similar to those of petroleum-based diesel and jet fuel.