The effect of thermal treatment on the surface properties of silica gel was investigated by the gas phase titration method. The silica gel samples were heated at 200, 400, and 800 degrees C. Ethyl methyl ketone was applied as a blocking reagent, and n-octane, benzene, and chloroform were used as testing probes. A new presentation of the results was proposed, which allowed their direct comparison for different sample areas. It was determined that the thermal treatment of silica resulted in different changes of testing probe retention upon adsorption of the same blocking reagent, and this was dependent on the type of surface-molecule interactions (nonspecific, electron-acceptor, and electron-donor, respectively). Certain differences in adsorption sites distribution were found. Then the changes in free enthalpy of adsorption were calculated for all testing probes. The results are discussed in terms of condensation of surface silanols and formation of siloxane bridges.