The degree to which molten silicon wets a solid, and reacts chemically and physically with it, determines the solid's usefulness as a die or container material. It is the purpose of this work to show that the oxygen partial pressure in the environment is an important factor in determining the degree to which solids are wetted by liquid silicon. Of particular interest is the PO2 range below where SiO2 is formed. In a recent study1 the authors have demonstrated that the oxygen activity in this range is very significant in determining both the chemical and physical interaction and the contact angle between liquid silicon and some refractory solids. The PO2 dependence of the contact angle is then used to calculate the solid surface energies.