The efficiency of glow discharges in He, Ne, and Ar for the removal of H2O, CO, and CO2 from the surface of vacuum systems has been demonstrated. However, re-emission of the rare gas and of hydrogen atoms trapped in the surface during the discharge cause the total outgassing rate not to be significantly reduced. In general, as the pressure of the discharge increases, the efficiency of cleaning decreases, and this has been correlated with a decrease in the number of energetic ions hitting the surfaces.