Kongsberg Silver Mines
The silver mines of Kongsberg, in Buskerud county in Norway, constitute the largest mining field in Norway, with over 80 different mines. It was the largest pre-industrial working place in Norway, with over 4,000 workers at its peak in the 1770s and supplied over 10% of the gross national product of the Danish–Norwegian union during its 335-year-long history: over 450,000 man-years were expended in the production.
Norwegian Sea
The most important products of the Norwegian Sea are no longer fish, but oil and especially gas found under the ocean floor. Norway started undersea oil production in 1993, followed by development of the Huldra gas field in 2001. The large depth and harsh waters of the Norwegian Sea pose significant technical challenges for offshore drilling. Whereas drilling at depths exceeding 500 meters has been conducted since 1995, only a few deep gas fields have been explored commercially. The most important current project is Ormen Lange (depth 800-1,100 m), where gas production started in 2007. With reserves of 1.4 cubic feet, it is the major Norwegian gas field. It is connected to the Langeled pipeline, currently the world's longest underwater pipeline, and thus to a major European gas pipeline network. Several other gas fields are being developed. A particular challenge is the Kristin field, where the temperature is as high as 170 °C and the gas pressure exceeds 900 bar (900 times the normal pressure).
Further north are Norne and Snøhvit.