During the process of hydrogen plasma smelting reduction (HPSR), hydrogen in the plasma state reduces iron oxide in a plasma arc reactor. In HPSR, a mixture of H2-Ar or H2-N2 is injected into the plasma arc zone. The main thermophysical properties of the plasma gases are the transport coefficients and heat and mass transfer, which are the main parameters that influence the ionization degree and consequently the reduction rate of iron oxides. In this study, the transport coefficients of argon, nitrogen, hydrogen, and mixtures of argon-hydrogen and nitrogen-hydrogen are discussed. The properties of plasma gases in terms of viscosity, thermal and electrical conductivity, and heat capacity are also presented. Moreover, the energy demand of steel production with the use of different plasma gases is evaluated and compared. The gas compositions of H2-Ar and H2-N2 mixtures at high temperatures were calculated by FactSageTM 7.1