When the facility was established - in 1977 - it was expected to have a working life of perhaps 25 years.
But now Repsol Sinopec says it expects the site to have a productive future up until the early 2030s.
Managing director Bill Dunnett told BBC Radio Orkney: "We're here for the long term. We believe in the North Sea. This is a core asset for the whole country."
Production at the plant is now running at around 100,000 barrels of oil a day - around a quarter of what it was in the late 1970s.
But Bill Dunnett said those statistics don't tell the whole story.
"If you look back five years ago the forecast for now was about 15,000 barrels a day. And we're doing 100,000.
"So I think it's very difficult to put a cap on what the production levels will be here.
"But our goal is to keep the level high, and keep this a viable asset for the future."
One key client for the site is the Golden Eagle field - responsible for about three quarters of daily production.
Area development manager for Nexen, Glen Brook, said the company had a "good partnership" with the team at Flotta.
"We've built a good operational relationship with them over the last three years since we started producing oil here.
"We're really pleased with the relationship...and we do see a bright future."
Two people who'll be hoping that's right are new apprentice Jennifer Atkinson, and Chris Adam who completed his four years ago.
"It was just a general oil and gas apprenticeship I applied for", Chris said.
"I think they saw my address was Thurso, and someone thought that's right next to Orkney. We'll put him to Orkney. But, it's worked out for the best. This is probably the best place to do your apprenticeship."
Jennifer said she was confident she'd see out her career in the industry.
"There's so many opportunities throughout the world as well, if it was to decline (here)."
The oil terminal at Flotta in Orkney is celebrating its 40th anniversary.