The first gas has begun flowing to the mainland from vast reserves west of Shetland.
A gas plant in Shetland has been fired up by Total, capable of supplying energy to up to two million homes.
A flare was lit at the moment that gas started flowing from the Laggan and Tormore fields, 125km north west of the Shetland.
The island plant has been the biggest construction project in the UK since the London Olympics.
West of Shetland contains almost one fifth of the UK’s remaining oil and gas reserves.
Total said the Laggan and Tormore fields will produce 90,000 barrels of oil equivalent per day.
From Shetland, a pipeline takes the gas back to the UK mainland and into the national gas grid.
It is expected to provide about 8% of the UK’s gas needs, supplying more than 2 million homes.
The project is part of a massive £3.5bn investment by French company Total. Challenging weather conditions delayed the project by more than a year and added millions to its cost.
The Laggan and Tormore fields are on the edge of the UK continental shelf, where water depths descend rapidly from an average of 120m to 600m and beyond.
Total said: “It’s a uniquely challenging environment in which to operate, but also one with great potential.”
The Shetland Gas Plant construction phase was estimated to have involved up to 800 jobs, with 70 full time posts in plant operation.
It has been built on a peat bog next to the Sullom Voe oil terminal.
As well as the onshore construction, there was a major programme of subsea infrastructure and pipelines.