"We are always treating situations when we observe oil on the sea seriously ... It's still too early to say the extent of this leakage," Eek said. Statfjord, which opened in 1979, is among the oldest fields still producing in the North Sea, and Equinor has said the first of its three platforms is due to close in 2022. "In compliance with regular procedures Equinor's emergency response organisation was quickly mobilised, and the authorities were notified," Equinor said. Statfjord is operated by state-controlled Equinor with a 44.3 percent stake, while ExxonMobil holds 21.4 percent and the rest is held by two units of Spirit Energy, data from Norway's Petroleum Directorate shows. (Reporting by Terje Solsvik and Victoria Klesty; editing by Jason Neely, Jane Merriman and Alexander Smith)