Vapour pressures of mixtures of octamethylcyclotetrasiloxane + benzene and octamethylcyclotetrasiloxane + carbon tetrachloride have been measured at 25, 35, 45, 55, and 60°C by a precision static vapour pressure method. For the first system the excess entropy and excess enthalpy are independent of temperature. Excess volumes at 25 and 60°C are also presented; for this system they are small and negative. Results for the second system will require calorimetric studies to finalize conclusions because of uncertainties in the second virial coefficients of carbon tetrachloride. The excess volumes for this system were also negative but larger in magnitude.