This consultancy project focused on the measurement and modeling of thermophysical properties for various blends of hydrogen-natural gas (H₂-NG) mixtures. At the request of the client, Wood Group UK Ltd, three specific blends containing 5%, 20%, and 80% molar concentrations of H₂ were tested. The project involved measuring the density and speed of sound for these blends. Using the measured properties, additional thermophysical properties such as isochoric and isobaric heat capacities, as well as Joule-Thomson coefficients, were derived.