High-pressure phase behaviour data are reported for the binary systems CO2 + N-[3-(trimethoxysilyl)propyl]aniline (TMSPA) and CO2 + (3-mercaptopropyl)trimethoxysilane (MPTS). The organosilanes TMSPA and MPTS are employed to functionalise with the amino and mercapto groups, respectively, the surface of inorganic materials using supercritical CO2 as a solvent and reaction medium. The measurements were conducted in a high-pressure variable volume view cell at T = 313.2, 323.2, and 333.2 K and pressures up to p = 25.0 MPa. The CO2 mole fraction in the binary mixture was varied from 0.40 to 1.0. For both silanes, the immiscibility region enlarges as the temperature rises. For a given pressure and temperature MPTS is considerably more soluble in CO2 than TMSPA. For instance, if a temperature of 313.2 K is chosen a pressure of 8.7 MPa will suffice to assure the solubilisation of MPTS in the whole mole fraction range whereas a pressure of 21.0 MPa will be necessary for the solubilisation of TMSPA. The Peng-Robinson equation of state was used to correlate the phase equilibrium data.