High pressure differential scanning calorimetry was utilized to study the mass transfer rates across methane hydrate films grown at hydrocarbon-water interfaces in a quiescent system, as a function of subcooling and the age of the film. Gas hydrate films formed at such interfaces provide a substantial barrier to further gas hydrate formation. The initially high mass transfer rates across the gas hydrate films formed at gas-water interfaces confirmed that the films were porous in nature containing varying degrees of porosity, with the films requiring Up to >24 h to anneal. Conversely, films formed at water-liquid hydrocarbon interfaces exhibited much lower mass transfer rates. The mass transfer rate is also dependent on the formation conditions of the film and is at a maximum at around 22 K of subcooling. This maximum appears to be independent of gas hydrate structure and pressure.