Coal produced in Korea is primarily anthracite supplemented by small amounts of Tertiary lignite. The anthracite beds are intercalated in Carboniferous, Permian, Jurassic, and Cretaceous rocks; the most productive beds are in the Permian. Nine of the 11 anthracite fields are aligned in the Ogcheon geosynclinal zone, from the middle east cost to the southwest coast of the Korean Peninsula. Anthracite reserves in southern Korea are estimated at 1.45 billion MT, of which 90% is Permian and 10% Jurassic. Annual anthracite production in Korea has been 10-14 million MT for several years. Calorific value of the Paleozoic anthracite is 5,500-6,000 cal (9,900-10,800 Btu), and the value for Mesozoic coal is 5,000-5,500 cal (9,000-9,900 Btu), with some exceptions of 6,000-6,500 cal 10,800-11,700 Btu). Prospecting for anthracite beds is being carried out by detailed geological and geophysical surveys and by care boring of drifting.