Energy company Total has announced a major gas discovery off Shetland.
Initial tests at a site on the Glendronach prospect indicated there could be about one trillion cubic feet of gas which could be extracted.
Total's Arnaud Breuillac said the discovery could be commercialised by using the current Laggan-Tormore infrastructure.
Total has a 60% stake in the site. Energy company SSE and chemicals firm Ineos each have a 20% interest.
Mr Breuillac, Total's president of exploration and production, said: "Glendronach is a significant discovery for Total which gives us access to additional gas resources in one of our core areas and validates our exploration strategy.
"Located on an emerging play of the prolific west of Shetland area, the discovery can be commercialised quickly and at low cost."
The Greater Laggan area is about 125km (78 miles) north west of Shetland.
Deirdre Michie, industry body Oil and Gas UK's chief executive, said: "This is a major discovery by Total which demonstrates the exciting potential the West of Shetland frontier region holds."
Global energy consultancy Wood Mackenzie said it was the largest conventional gas discovery in UK waters since Culzean in 2008 in the North Sea. A trillion cubic feet of gas equates to 176 million barrels of oil equivalent.
Kevin Swann, senior research analyst, said: "Exploration in the UK has been a huge concern so far in 2018 with just five exploration wells spudded to date - on track for lowest levels of activity since the 1960s.
"So this discovery is welcome news, even if there is more work to do if the UK is to fill the project gap that is set to arise in the next few years. The cupboard is pretty bare beyond 2020."
However, Friends of the Earth Scotland director Dr Richard Dixon said: "This exploitation of this new gas discovery off the coast of Shetland is incompatible with a country and a world that takes climate action seriously.
"This gas should stay where is it."