Abstract: Energy and environment concerns are becoming more and more urgent for the existence and progress of human society. Clathrate hydrates hold great promise in a number of aspects: (1) vast methane hydrate deposits have been found in the continental shelf around the world; (2) oceanic sequestration of CO2 may be a feasible approach to reduce the greenhouse effect; (3) hydrogen clathrate hydrates of high energy density are readily rechargeable; (4) clathrate hydrate processing is a very effective way for gas separation and is great for energy saving and emission reduction. Despite the engineering and scientific importance of clathrate hydrates in energy resources and environmental aspects, much remains to be learned about their crystal structures, molecular bonding mechanisms, P-T phase diagrams, formation/decomposition kinetics, thermodynamic and mechanical stabilities, and acoustic (seismic) elasticity. Recent experimental studies of H2, CH4, and CO2 clathrate hydrates have been integrating neutron diffraction, laser spectroscopy, thermal analysis, and ultrasonic experiments at moderate (1 to 100 MPa) to high (0.1 to 1 GPa) pressures, and great progress has been made in the studies of their crystal comstructure, occupation of gas molecules in the hydrate cages, as well as their temperature-pressure phase diagrams.