A new equation of state for the thermodynamic properties of natural gases and other mixtures was developed. The new formulation is a fundamental equation explicit in the Helmholtz free energy as a function of density, temperature, and composition. The
model uses accurate equations of state for each mixture component along with functions that take into account the mixture behaviour. The equation covers wide ranges of temperature, pressure, and composition and is valid in the gas phase, liquid phase,
supercritical region, and for vapour-liquid equilibrium states. The model achieves a high accuracy in the calculation of thermodynamic properties for a broad variety of mixtures. The wide range of validity enables the use of the equation in both standard
and advanced technical applications for natural gases and related mixtures, including processing, transportation through pipelines or by shipping, and storage of natural gas, as well as future applications with natural gas/hydrogen mixtures.