In order to have an improved understanding of the applicability of standard EOS in pipeline applications, a set of gas physical property tests were undertaken with sweet and sour natural gas and CO2 mixtures at typical pipeline compositions and conditions, including new high pressure dense phase applications. Specific gas properties tested include gas density (ρ), specific heat at constant volume (cv), and speed of sound (c or SOS). These results were compared to several of the most commonly used EOS, including NIST, GERG, AGA8, PR, SRK and BWRS, which were also compared to each other.