A second‐order group additivity method has been developed for the estimation of the heat capacity of liquid organic compounds containing carbon, hydrogen, halogens, nitrogen, oxygen, and sulfur. The method permits the estimation of the heat capacity as a function of temperature in the range from the melting temperature to the normal boiling temperature. Group contributions and structural corrections have been made temperature dependent by the use of a polynomial expression. The adjustable parameters in the polynomials have been calculated using a weighted least squares minimization procedure. This work has drawn information for both the development and testing of the method from a large compilation of critically evaluated heat capacity data for over 1300 organic liquids.