Experimental liquid densities and compressibility factors of natural gas and liquefied natural gas mixtures were reproduced using an analytical equation of state, based on the statistical-mechanical perturbation theory of Weeks, Chandler and Andersen. The temperature-dependent parameters of the equation of state were calculated using our previous corresponding-states correlation, based on the normal boiling point parameters. This article shows that the equation of state for multicomponent natural gas and liquefied natural gas mixtures would be predictable with minimal input information, namely the normal boiling temperature and the liquid density at the normal boiling point. The calculated results agreed well with the experiment. From a total of 590 data points for natural gases and 203 data points for liquefied natural gases examined in this work, the average absolute deviations were 0.33% and 2.48%, respectively, and the maximum deviations were 2.63% and 4.61%, respectively.