In February 2007, he finished fifth at the Korea Pro Pool Tour, and ninth at the Predator International Championship.

[3] In November 2008, Ōi achieved his biggest international success so far: he reached the semi-finals of the All Japan Open, finishing third.

At the 2012 WPA World Nine-ball Championship, Ōi had victories against Chang Jung-lin, Thorsten Hohmann, and Karl Boyes to reach the semifinals before losing to eventual champion Darren Appleton, who defeated him 7–11.

Ōi, who speaks little English, responded to a question with lyrics from the song "Pen-Pineapple-Apple-Pen" by comedian Daimaou Kosaka.

First appearing in the 2007 tournament along with partner Satoshi Kawabata, Oi reached the semi-final, losing to champions Li Hewen and Fu Jianbo.