Óscar Pereiro Sio (born August 3, 1977 in Mos, Galicia) is a Spanish professional road bicycle racer best known for winning the 2006 Tour de France after the original winner, Floyd Landis, was disqualified for failing a series of doping tests. Pereiro currently rides for the Caisse d'Epargne cycling team. He is a former member of the Portugal-based team Porta da Ravessa (2000 to 2001) and the Swiss-based team Phonak Hearing Systems (2002 to 2005).
Pereiro placed tenth in the 2004 Tour de France, 22 minutes 54 seconds behind Tour winner Lance Armstrong. He was awarded the Most Aggressive Rider Award in the 2005 Tour de France after powering the winning breakaways in Stages 15, 16 and 18. He was the Stage 16 winner - just edging out Spain's Xabier Zandio, Italy's Eddy Mazzoleni and Australia's Cadel Evans. His efforts on Stage 15, the toughest stage of the Tour, were highly admired by the peloton. He finished second that day to Discovery Channel's George Hincapie after "pulling" for most of the final climb up the Pla D'Adet.
Pereiro was considered a leader on Phonak along with Landis and Santiago Botero in 2005 - his last year riding for the team.