First oil flows from redeveloped Schiehallion field
The first oil has been produced from the redeveloped Schiehallion field, which BP says could unlock 450 million barrels.
Schiehallion - 110 miles west of Shetland - has been shut down for refurbishment since 2013.
The Quad 204 project aims to breathe new life into the Schiehallion and neighbouring Loyal fields, which were first developed in the 1990s.
It could extend the life of the fields to at least 2035.
Bob Dudley, BP Group chief executive, said: "The start of production from Quad 204 - one of the largest recent investments in the UK - is an important milestone for BP, marking a return to growth for our North Sea business."
It has included the construction of the floating, production, storage and offloading (FPSO) vessel Glen Lyon to be capable of meeting the demands of the project.
Deirdre Michie, chief executive of industry body Oil and Gas UK, said: "This is excellent news and another positive endorsement of the potential the UK Continental Shelf (UKCS) still offers with the right investment.
"It's also extremely heartening to see one of the original explorers of the basin using new, ambitious approaches and pioneering technology to help lead a revival in production.
"As well as being a welcome boost for the hard pressed supply chain, the announcement from BP and co-venturers Shell and Siccar Point Energy, proves that our faith in the long term health of the basin is well founded. "
The announcement was also welcomed by Scottish Energy Minister Paul Wheelhouse, who said: "This is a key milestone in BP's plans to double North Sea production by 2020 and reflects the company's long-term commitment to the North Sea."