We had very remarkable results from the CHAOS-1 (2003) and CHAOS-2 (2005) project; lots of gas flares in the water column, many gas venting structures on the seafloor, gas hydrate samples including massive gas hydrate chunk (about 45 cm thick) near the seafloor, and gas hydrate-related structures in deep sub-bottom depth. These results encourage us to continue and expend the CHAOS project. Since the previous expedition focused on the relatively small area where gas hydrate-related phenomena has been known to be active, the basic aim of the CHAOS-III expedition is to improve understanding on gas hydrate-related phenomena in the Sea of Okhotsk in terms of multidisciplinary areas including geology, chemistry, oceanology and biology. 1. Detection of new gas hydrate-related structures including gas flares and gas venting structures. 2. Definition of the boundaries of the gas hydrate province 3. Mapping of the seafloor expressions related with gas hydrates and gas seepages using side-scan sonar. 4. Recognition of size, shape, and morphology of gas seepages on the seafloor. 5. High-resolution seismic investigation to examine inner structures and the gas hydrate stability condition in gas hydrate-baring sediments in detail. 6. Detection of gas flares in the water column emitted from gas seepages. 7. Study on hydrated water and dissociated gas sample 8. Chemistry of gas, gas hydrate, hydrate-forming fluids and carbonates including isotopic analysis. 9. Determination of methane concentration in the water column. 10. Underway survey to understand distribution of methane and dioxide in surface water and its controlling factor. 11. Detailed investigation of marine sedimentological environment in the gas hydrate area 12. Mechanism of formation-dissociation for gas-hydrates. 13. Interrelation of methane fluxes and mercury 14. Organic geochemical information related to the origin and composition of sedimentary organic matter. 15. Identification of biomarkers of microorganisms associated methane cycle. 16. Understanding of the composition of microbial community in gas hydrate environment