Hot on the heels of the marquee signing of Mark Cavenish from the defunct HTC-Highroad team, Flecha (pictured) and Knees penned two-year deals while Barry extended his current agreement by 12 months.
Team Sky and Team GB performance director Dave Brailsford called the trio “world class” in expressing his delight at the deals.
"At Team Sky we are always striving to improve as a team and retaining our key riders is a vital component of that strategy," he said in a statement. "We are delighted that three world-class talents in Michael, Christian and Juan Antonio have seen Team Sky as the best place to continue their careers.
"As athletes, their records at the very highest level of our sport speak for themselves. As senior professionals they have set a standard of behaviour that is an inspiration to our younger riders.
"All three have contributed hugely to our success as a professional team and we all look forward to continuing that momentum into 2012 and beyond."
Flecha, who is regarded as a top one-day rider, said he was looking forward to the whole season.
"I am really happy to be riding for the team again next season," he said. "The improvements we have made over the last year have been testament to the amount of work we have put in and I am really excited about what 2012 will bring.
"The cobbled Classics will be my main focus, as always, but I am also looking forward to helping the team throughout the rest of the season."
Barry said: "I've enjoyed being a part of the development and growth of the team in the last two years and am looking forward to another season with Team Sky. To me, the environment is ideal: the team is well organised, the management is solid, the staff is committed and we have a great ambience amongst the riders.
"All of the guys enjoy racing and being together which, in the end, produces results. I'm happy and proud to be a member of the team."
Knees added: "I've had a great first season with Team Sky, and a lot of happy memories, so when the offer of a new deal arose I signed straight away." . "To make the Tour de France team was amazing, especially after joining the squad so late, and I've been really happy with the role I've had to play in the team.
"I hope I can show my best over the next two years now, and when I'm not working for the other riders it would be nice to try and get a win for myself to repay the faith they have shown in me."