A wide application of hydrogen energy is seen as a viable strategy to reduce the excessive release of CO2 in the atmosphere. Large demand requires the hydrogen to be distributed through pipelines. While blending hydrogen into existing natural gas pipelines is recommended as a transition option to progressively increase the energy share of hydrogen, it is important to develop a better understanding of the decompression characteristics of Natural Gas-Hydrogen (NGH2) mixtures, to ensure that the pipelines are capable of arresting a running ductile fracture. In this paper, Computational Fluid Dynamics (CFD) models incorporating the Peng-Robinson (PR) Equation Of State (EOS) were used to simulate the decompression of NGH2 mixtures. The PR EOS was extended to gas mixtures using the van der Waals mixing rules and three types of combining rules. Two shock tube tests were modelled to validate the performance of the PR EOS with different combining rules. The model was also validated through comparison with the GERG-2008 EOS. In addition, decompression characteristics of a typical NG blended with 0%���30% hydrogen were studied.