Oceansize are a five-piece rock group formed in Manchester, England, in 1998. The band consists of Mike Vennart (vocals, guitar), Steve Durose (guitar, backing vocals), Richard "Gambler" Ingram (guitar, keyboards), Mark Heron (drums) and Steve Hodson (bass). To date, the band have released four studio albums in addition to a number of minor EPs and singles. The band can be categorized variously as progressive rock, post-rock, alternative rock, new prog and space rock, among other genres.

The band is named after the Jane's Addiction song "Ocean Size". According to guitarist Gambler, the band's former bassist came up with the name: "I think, at the time, he was thinking what we would sound like. Jane’s Nothing's Shocking album, which has the track "Ocean Size" on it, was definitely a big influence."