The second generation High Pressure Automated Lag Time Apparatus (HP-ALTA MkII) was used to measure the nucleation curves of Structure II (sII)-forming methane-propane mixed gas hydrates on the surface of a quasi-free water droplet suspended in involatile hydrocarbon oil, squalane. The measured nucleation curves were then compared to the previously obtained nucleation curves of the same guest gas hydrate on a quasi-free water droplet supported by perfluorodecalin. The comparison of the two sets of data sets showed that the nucleation rates of the two systems were broadly similar to each other. A simple master nucleation curve was derived for each system as a function of the system subcooling. The model-independent empirical equation that relates the nucleation rate to the system subcooling was J(water-guest) (S-1 m(-2))=2.38 x 10(-39) Delta T-26.746 for a quasi-free water droplet suspended in squalane and J(water-guest) (S-1 m(-2))=7.70 x 10(-11) Delta T-7.931 for a quasi-free water droplet supported by perfluorodecalin. The nucleation rates predicted by these empirical equations are then compared to the nucleation rates of other relevant systems in the literature. The model-independent analysis method for the derivation of nucleation curves we have developed can be applied to constant cooling ramp data obtained by any experimental techniques. (C) 2016 Elsevier Ltd. All rights reserved.