Low oil saturating vapor pressure: This oil characteristic is essential in order to achieve the desired vacuum. Specific base stocks are used to formulate these products. High resistance to oxidation: It allows to avoid organic deposits formation. Good viscosity index: Low variation of viscosity due to temperature increase, steady during the whole oil service life, thus assuring sealing performances of the vacuum pump. In case of corrosive gas or very advanced vaccum, specific fluids are required (polyethers, silicones...).