The present work examines the host-guest interactions in H-2-THF mixed hydrates in a fused dodeca-hexakaidecahedral cage at the molecular level. The host-guest interaction energies are analyzed to get insight on the occupancies of H-2 and THF in different host cages. The maximum and optimum storage capacity of H-2 in dodecahedral and hexakaidecahedral cages is determined. The studies show that THF in a hexakaidecahedral cage interacts with water molecules of the neighboring dodecahedral cage whereas H-2 due to its smaller size does not interact with water molecules of a neighboring cage. The interaction energy and free energy associated with the encapsulation of guest species revealed that simultaneous encapsulation of H-2 and THF in the large cavities of sII hydrates is feasible. Energy decomposition analysis indicates that electrostatic and dispersion interactions contribute significantly to the stability of the complexes. The occupancy of H-2 in small and large cages of mixed hydrates are analyzed in terms of H-1 and C-13 chemical shifts. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.