Oshima is one of only two drivers that have won championships in both classes of Super GT, having won the GT300 Drivers' Championship in 2007, and the GT500 Drivers' Championship in 2019. He also won the 2009 Suzuka Summer Endurance race. Outside of Japan, is a five-time class winner at the Nürburgring 24 Hours (2010, 2012, 2014, 2015, 2016) as a member of Gazoo Racing/Toyota Gazoo Racing.
Oshima made his GT300 debut with APR, with Minoru Tanaka in 2006. Then he won the title in 2007 with APR alongside Hiroaki Ishiura. For 2008, he made a one-off appearance with APR.
Supet GT GT500
Oshima returns to Japan in 2009, and he stepped into GT500 with Team Kraft alongside his former GT300 Champion teammate Ishiura. He racef there for 2 seasons where he won 2 races in each year. After that he moves to Team LeMans to pair with Daisuke Ito for two years, where both pairs only get one win in 2012. Then he paired with Yuji Kunimoto for over three years. From 2016 & 2017, his new teammate Andrea Caldarelli with him clinched runners up, and third place in 16 and 17.[2][3] Then Oshima paired with Felix Rosenqvist for one season. In 2019 Oshina alongside Kenta Yamashita won the title against the KeePer TOM'S of Ryo Hirakawa and Nick Cassidy.[4]
After won the title, Team LeMans left the series. And Oshima moves to the new entrant Rookie Racing with new teammate Sho Tsuboi.[5][6] Then he is the mainstay of Rookie Racing, where he paired again with Kenta Yamashita for 2022 & 2023 where they won one race each season. Oshima then paired with former Honda driver Nirei Fukuzumi for 2024.[7]
Super Formula
Oshima made his Formula Nippon debut in 2009 after return from unsuccessful season in Europe, where he moves to Petronas TOM'S for two seasons. In 2010 he won a race. Then in 2011 he moves to Team LeMans for two seasons. After that he did not compete in the series for four seasons, except one-off appearance in 2015 as he replaces Kazuki Nakajima for one race. Oshima comes back to the rebranded Super Formula, as he returned to his former Team LeMans to race for 3 seasons. After Team LeMans stop their operation in Super GT & Super Formula, Oshima moves to Rookie Racing.[8][9] Then Oshima stays with the team for five seasons.