To develop gas hydrates as a potential energy source, geophysical and geological studies were carried out in the Ulleung Basin, East Sea. Bottom simulating reflectors (BSRs) were initially used indicator for the potential presence of gas hydrates across the basin. Based on these early results, 12367 line-km of multichannel seismic data, 38 piston cores, and multibeam data were collected. The cores showed high amounts of total organic carbon and high residual hydrocarbon gas levels. Gas composition and isotope ratios define it as of primarily biogenic origin. In addition to the BSRs, numerous chimney-structures were found in seismic data. These features indicate a high potential of the Ulleung Basin to host significant amounts of gas hydrate. Dedicated geophysical surveys, geological and experimental studies were carried out culminating in two deep drilling expeditions, completed in 2007 and 2010. Sediment coring (including pressure coring), and a comprehensive well log program complements the regional studies and were used for a resource assessment. Two targets for a future test-production are currently proposed: pore-filling gas hydrate in sand-dominated sediments and massive occurrences of gas hydrate within chimneylike structures. An environmental impact study has been launched evaluating any potential risks to production.