Abstract Second and third virial coefficients ( B and C ) for the T range from about the critical temperature to the Boyle temperature are presented for argon, carbon dioxide, ethane, hydrogen, methane, nitrogen, oxygen, and propane. That these virial coefficients are more reliable than those previously available is demonstrated by the ability of the new B and C by themselves to represent the equation of state of these gases in the extensive LISOK region, which is defined as the PVT region in which T versus ρ at constant K = ( Z − 1)/ ρ is observed to be linear.