To date the Thermodynamic Difference Rule (TDR) has proved itself to be highly satisfactory as ameans of establishing unknown thermodynamic data. In Parts 1 (Jenkins, 2017) and 2 (Jenkins, 2017) we demonstrated the successful prediction of Delta H-f(o) data for gas clathrate hydrates using TDR. In the absence of any experimental standard Gibbs free energy, Delta(f)G(o) or standard entropy, S-298(o) data suggestions were made (based on experience with conventional inorganic hydrates) of likely forms of TDR equations which might predict these missing thermodynamic values. In the present paper, in view of the availability of a few experimental heat capacity values, we test the applicability of a similar suggested form of TDR for C-p prediction against the experimental values. Despite the fact that an absolute comparison cannot actually be achieved, closeness of predicted and (extrapolated) experimental values compare well. The result suggests that our previous TDR equations for the prediction of Delta(f)G(o) and S-298(o) are likely to be highly reliable. (C) 2017 Elsevier Ltd.