He finished overall third in the Orienteering World Cup in 2004, and has a silver medal in relay from the 2004 World Ski Orienteering Championships. Østerbø finished third overall at the 2004 Orienteering World Cup, with a total score of 207 points (same score as Russian Andrey Khramov who finished second).
He was ranked 7th in the World Cup 2005. In 2008 in Ventspils he made a small mistake that cost him the medal in the sprint distance, where he finished 8th but missed the bronze medal by only eleven seconds. At this championship he finished 8th in the sprint distance and 6th in the middle distance.
He received a bronze medal in relay at the European Orienteering Championships in 2006 in Otepää. He has been Norwegian champion in night orienteering since 2006. Østerbø participated on the Norwegian team that received a silver medal at the World Ski Orienteering Championships in 2004, together with Anders Hauge, Eivind Tonna and Tommy Olsen.
