OIL companies BP and its partners Shell, ConocoPhilipps and Chevron have announced further investments of £330 million into the Clair oil field, 75 kilometres west of Shetland.
The consortium said it would be drilling up to 12 new wells to further appraise the giant oil field that is holding around eight billion barrels of reserves.
Oil production at Clair started in 2005, almost 30 years after its discovery.
Last year BP announced that it would spend £4.5 billion into developing phase two of the project.
This latest investment could lead to phase three taking oil production well beyond 2050, and securing the future of the Sullom Voe terminal until that time.
BP North Sea regional president Trevor Garlick said: "This is a major milestone and a further big commitment to the west of Shetland by BP and its co-venturers.
"If successful, the appraisal programme could pave the way for a third phase of development at Clair - this is now a real possibility."