For the production of high purity special alloys, a melting and treatment in the vacuum induction furnace (VIDP) is especially important. The aims of this paper are a detailed description as well as a deeper theoretical understanding of vacuum metallurgy and vacuum carbon deoxidation in the VIDP while paying special attention to process equilibria and limitations. The contents of oxygen, carbon and nitrogen of five different alloys, covering a carbon content from 0,001 to 0,82%C, were examined at four definite times in the refining phase. Experiments verified that the melt is in the process equilibrium at the end of refining. Thereby the CO process equilibrium ranges at 1mbar when analysing alloys with lowest C content. A product a[C]*a[O] up to 10^-6 can be determined at the refining end. Since the low CO partial pressures, which appear with lowest C-contents, result in a strong reduction potential, Al2O3 and MgO with CO partial pressures below 5,33mbar (with 1600°C) are already reduced resulting in a constant oxygen delivery.This implies that vacuum carbon deoxidation is completely put to the extreme, seeing that for thermodynamic reasons no lower values can be reached. These results are compared and discussed with the theoretical equilibria calculations and values from the literature.