Thermodynamic processes, occurring in three-phase system of metal-gas-crucible, are investigated via physical experiment. The alloys of systems Fe-C, Fe-C-Si, Ni-Fe-Cr-C are melted in aluminum or beryllium oxide crucible with molybdenum heater. Oxygen content in gas phase is no more than 0.003%. It is ascertained that the oxygen behavior in melt is being caused, mainly, the kinetic characteristics of oxygen transfer processes from crucible into melt and its release into gas phase.