This study presents measured densities, viscosities, speeds of sound, surface tensions, and flash points and calculated bulk moduli of mixtures of 2,2,4,6,6-pentamethylheptane with C9H12 isomers (1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, and n-propylbenzene). The densities, speeds of sound, bulk moduli, and surface tensions increase and viscosities decrease as the mole fraction of the C9H12 isomer increases. Flash points decreased, remained the same, and increased as the amounts of n-propylbenzene, 1,3,5-trimethylbenzene, and 1,2,4-trimethylbenzene increased, respectively. Ideal behavior was found for viscosity, in which the excess molar Gibbs energies of activation for viscous flow did not differ statistically from zero. Nonideal behavior was found for excess molar volumes, V-m(E), and excess speeds of sound, c(E), which were positive for all mixtures. Molecular dynamics (MD) simulations were used to predict the densities, bulk moduli, surface tensions, and viscosities of these binary mixtures. Although the densities, bulk moduli, and surface tensions were correctly reproduced, the simulations predicted nearly constant viscosities as a function of composition. The MD simulations showed that the molecular-level fluid structure of n-propylbenzene differed from that of 1,3,5-trimethylbenzene and 1,2,4-trimethylbenzene and that the preferential orientation of the aromatic rings of all three molecules was disrupted upon mixing with 2,2,4,6,6-pentamethylheptane. Finally, the mixtures showed an enrichment of 2,2,4,6,6-pentamethylheptane near the liquid-vapor interface. This interfacial enrichment depended on the mixture composition, with high C9H12 mole fractions leading to a larger degree of 2,2,4,6,6-pentamethylheptane enrichment at the interface.