This paper describes an experimental approach to the competitive adsorption of two different vapor molecules at room temperature on natural solids. We report firstly the isotherms of benzene, tetrahydrothiophene (THT), and water on quartz at 25 degrees C. The isotherms of water and THT present a hysteresis. The adsorption of benzene is fully reversible. Secondly we present results of adsorption of one vapor on a solid precovered by the other molecule. In this latter experiment, the quartz is covered by a chosen quantity of statistical layers of water (or benzene or THT). Another vapor species is then introduced in the closed experimental system. Our experimental device allows the displacement of both molecules to be followed. The first important conclusion in the analysis of the displacement of water by benzene is the fact that the displacement depends on the precoverage value. If the coverage is greater than 1 statistical monolayer, it is necessary to increase the partial pressure of benzene up to a "critical" value, in order to displace a small quantity of water from the quartz. The benzene is displaced by water in the very low partial pressure region, compared to previous results of displacement of water by benzene. The individual and composite adsorption isotherms of one component in the presence of the second are compare d. In this latter case, the quantities of adsorbed water are greater than those obtained in preceding experiments. The displacement of preadsorbed THT by water is impossible in the studied range of pressure.