We studied the growth rate of methane propane mixed gas hydrate films on the surface of water and up to 3 wt % aqueous solutions of a kinetic hydrate inhibitor, Luvicap EG. The greater the subcooling, the faster the growth rate of the hydrate film on water. Using Mori's heat-transfer-limited growth model, we estimated the initial thickness of the hydrate films on water to be between 1.3 and 25 mu m. The addition of Luvicap EG inhibited both the nucleation and the growth of the hydrate films, because we observed that the films on Luvicap EG solutions grew slower and their nucleation required greater subcoolings than those on water. Notably, the hydrate films that grew on Luvicap EG solutions were more transparent and, thus, thinner than those on water. The thinner and yet more slowly growing hydrate films on Luvicap EG solutions suggest that the growth mechanisms had changed from heat-transfer-limited growth to mass-transfer-limited growth.