PVT relationships of two binary mixtures of indole with 2-methylnaphthalene and with biphenyl have been measured at 333.15 K and at pressures up to 270 MPa or up to near the freezing pressure of each mixture. The compositions in mole fraction of indole were set to be 0.2500, 0.5000, and 0.7500 for both systems. PVT relationships of indole (at 343.15 K and 353.15 K), 2-methylnaphthane (at 333.15 K and 343.15 K), and biphenyl (at 353.15 K and 363.15 K) under pressure and those for the binary mixtures at 0.1 MPa in the temperature range from 293.15 K to 363.15 K were also measured. PVT data were analyzed with the use of the Tait equation and Carnahan–Starling–van der Waals (CS–vdW) equation. It was found that both the equations can be used to represent the experimental PVT relationships for the pure compounds and the binary mixtures with an average absolute deviations of 0.04% for the Tait equation and 0.29% for the CS–vdW equation. As for mixture density calculations with the CS–vdW equation, the effect of mixing rules was investigated.