In general, oxygen can considerably change the wetting behavior of oxides by molten metals. This work is a basic illustration of the oxidation effect on the wetting behavior of glass by a liquid metal. Taking mercury as a model of a metal, the importance of the metal oxidation in the glass/metal interaction has been observed by measuring wetting contact angles of mercury on glass and the ability of calibrated mercury drops to slide down, under gravitation, on an inclined glass plate in air or in nitrogen. It is believed that the highest force of detachment by sliding of the mercury drop in air results from the metal oxidation which can be interpreted by a higher contact angle hysteresis a hen the metal is exposed to air.