We present a new and accurate extended corresponded states model for the prediction of thermodynamic properties of pure fluids. This model is based on shape factors expressed as functions of the reduced temperature and density, the acentric factor and the critical compression factor. Substance-dependent coefficients were optimised against volumetric, VLE and acoustic data for the light hydrocarbons from ethane to n-pentane, ethylene, nitrogen, carbon dioxide, oxygen, argon and carbon monoxide. With this model, fluid properties are estimated largely within their experimental uncertainty. The model was tested for reduced temperatures T-r in the interval 0.52 less than or equal to T-r less than or equal to 3.33 and for reduced densities up to 2.8. The work reported here is a necessary precursor to the development of an extended corresponding states (ECS) equation of state for natural gas systems and mixtures of natural gas constituents.