All three were used only sparingly by boss Roberto Mancini last season and their departures were expected, with the Italian set to bring in a number of players during the close season.
Petrov was signed by Sven-Goran Eriksson from Atletico Madrid in 2007 and enjoyed an impressive debut season on the wing.
But the Bulgarian's time at City was blighted by injuries and he leaves having made 57 starts, scoring 15 goals.
Striker Benjani was another Eriksson purchase, arriving from Portsmouth in January 2008 after netting on a regular basis during the first half of the season.
He made an instant impact by scoring the winner on his debut against Manchester United but he faded out of the picture and spent the end of this season on loan at Premier League rivals Sunderland, where he failed to score in eight matches.
Brazil defender Sylvinho joined City last summer after helping Barcelona win the Champions League but the 36-year-old was restricted to only nine starts.
Youngsters Jack Redshaw, Tobias Johansen and Karl Moore have also been released.