Crystal growth simulations of gas hydrates have suggested that hydrate cages may occasionally be occupied by H2O rather than guest molecules, leaving interstitial defects within the hydrate crystal. Further inspection of the behavior of these interstitial H2O molecules has revealed that they are relatively highly mobile entities within a gas hydrate. In this paper, we report these observations and examine the molecular mechanisms responsible for the transport of these interstitial molecules through hydrate crystals. Four distinct pathways for the H2O molecule transport between cages are found, each facilitated by the presence of empty cages. The relative richness of the observed behavior of interstitial defects suggests that interstitial diffusion could be an important mechanism for the mass transport of H2O molecules through gas hydrates.