Areas of major offshore development around the Korean peninsula are in the Yellow Sea off the west coast, in the East China Sea off the south coast, and in narrow belts in the Japan Sea off the east coast. Geological and geophysical surveys in these Korean offshore areas have been carried out since 1966 by the Geological and Mineral Institute of Korea (GMIK) and since 1969 by oil companies that obtained concessions on seven blocks from the Korean government.

The GMIK has conducted reconnaissance seismic and magnetic surveys for general study of submarine geology. Oil companies have conducted preliminary and detailed seismic, magnetic, and gravimetric surveys. Wildcat drilling was started in 1972, and four holes were drilled by three oil companies.

The Yellow Sea area contains a Tertiary sequence thicker than 1,000 m. several basin structures are separated by uplifted basement or intrusive igneous rocks.

The East China Sea and the southern part of the Japan Sea contain more than 2,000 m of Tertiary strata. The strata are folded and faulted and the structural trend is northeast-southwest.

In the rest of the Japan Sea area, Tertiary strata are present in the Pohang offshore area (<1,000 m thick) and extend northward for almost 100 km, whereas, on the continental slope, a 3,000-m-thick sequence is probably of Holocene age.

Petroleum potential in offshore Tertiary rocks is not well known. However, a high organic content increases the prospects in the Yellow Sea area, and the East China Sea and Japan Sea areas have good reservoir rock and structures favorable for hydrocarbon accumulation.