 Four appraisal wells drilled during 1971–1972 revealed a large reservoir at a depth of about and closure of 155 m. So marked the first and largest major oil field discovery in the United Kingdom sector of the North Sea.Oil had previously been discovered at the Ekofisk field.Named Forties because it lay just off the Long Forties Bank, the field began producing oil in September 1975 and was officially inaugurated by Her Majesty on 3 November 1975.