"Stability is key for any team to thrive in Formula One," said principal Frank Williams in a statement at the Italian Grand Prix.

"So to be able to enter a third season with one of the strongest driver line-ups on the grid puts Williams in a fantastic position to continue its momentum towards the front of the grid in 2016."

The decision means yet another unchanged lineup among the leading teams, with champions Mercedes and Ferrari having confirmed lineups and both Red Bull drivers under long-term contracts. Bottas had been strongly linked to Ferrari as a likely replacement for compatriot Kimi Raikkonen until the Italian team confirmed the 2007 world champion would be staying with them for another year.

There had also been speculation that 2009 world champion  Button could move from McLaren, who are having a nightmare season and have younger drivers knocking on the door, to Williams where he started his career in 2000.

Bottas could still be in the frame to move to Maranello in 2017, however, with the statement referring only to next year. "I am really pleased to be staying with the team for a fourth F1 race season," said the 26-year-old, who took a third place in Canada earlier this season.

"We have been getting stronger as a team and I look forward to what next year will bring, as I believe we can achieve even stronger results than what we have seen so far."

Massa, 34, had been expected to stay after joining from Ferrari in 2013. The Brazilian remains the last non-Mercedes works driver to take a pole position, in Austria last year, and has been on the podium four times for Williams.

"They respect me a lot and the results are there, and it has been so nice to be part of the big turnaround the team has seen since the end of 2013," he said.

Williams are third overall, where they finished last season, after scoring only five points and ending up ninth in 2013. "Both drivers have played a pivotal role in the rejuvenation of Williams," said Frank Williams. "The successes we've enjoyed over the past two seasons would not have been possible without them."

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