Oscarsson took a year off competitive canoeing in 2005. He returned to action in 2006 and won the K-1 1000 m bronze medal at the European Championships in Račice, Czech Republic - the first individual medal of his senior career. The following month he became K-1 1000 m world champion in Szeged, Hungary, edging out Britain's Tim Brabants by 0.06 sec. This was Sweden's first gold medal in canoeing's Blue Riband event since the late Gert Fredriksson's victory in 1954.
At the 2008 Summer Olympics, Oscarsson and Nilsson were disqualifed for leaving their lane. At the 2012 Summer Olympics, they again reached the final of the men's K-2 1000 m event, but finished in 5th place.
Oscarsson is 184 cm (6' 0) tall and weighs 84 kg (185 lb).