We present an extended corresponded states model for the prediction of thermodynamic properties of natural gas systems. This model is based on shape factors expressed as generalised functions of the reduced temperature and density, the acentric factor and the critical compression factor. A single set of coefficients was optimised for 12 major components of natural gases. The extension to multicomponent systems was carried out according, to the one-fluid model with temperature- and density-dependent binary interaction parameters. Compression factors and speeds of sound of natural gases were predicted with average deviations within +/-0.036%.