Thermodynamics of supersaturated (supercooled) steam at conditions occurring in steam turbines, and inaccessible thus to experiments, has been studied by a number of theoretical and semi-theoretical methods with the goal to assess available theoretical tools for developing an equation of state. Extended virial expansions with different reference systems have been used along with two, qualitatively different equations of state. According to the proposed strategy, all equations were first used for the vapor-liquid coexistence curve and then extended to the metastable region and tested against computer simulation data. Despite the fact that no specificities of supersaturated steam have been accounted for, all the considered methods provide results with deviations from (pseudo)experimental data up to about 5% over the entire range of thermodynamic conditions except the critical region. It turns out that the perturbed virial expansion with a suitably chosen reference system outperforms other methods, including equations of state originally developed for liquid water, (C) 2018 Elsevier B.V. All rights reserved.