This paper presents experimental results on the phase behavior of the binary system propane + triphenylmethane. Besides vapor-liquid equilibria, also equilibria in the presence of solid triphenylmethane have been determined experimentally. Special attention was given to determine the course of the various three-phase equilibria originating in the quadruple point solid triphenylmethane-liquid-liquid-vapor (s(B)l(1)l(2)g). The experimental work was performed in the temperature region 310 < T/K < 450, while pressures up to 11 MPa have been applied. Surprisingly, it was found that in this binary system the three-phase equilibrium liquid-liquid-vapor (l(1)l(2)g) could be determined at supercooled conditions over a temperature range of about 25 K, i.e. some parts of the fluid phase behavior could be observed and measured at metastable conditions.