"Two in a Million" is a song recorded by S Club 7, released as the third single from their debut studio album, S Club, on 13 December 1999. The single was released as a stand-alone single in Australia and the United States, but in the UK, was released as a double A-side with "You're My Number One". It made its debut at number 5 in the run-up to Christmas, selling almost 100,000 copies, but later peaked at number 2 on the UK Singles Chart in January 2000. It was the first single by the band to be released as a double A-side, later followed by "Say Goodbye" and "Love Ain't Gonna Wait for You" in 2003. "Two in a Million" is described as a slow ballad and has lead vocals sung by Jo O'Meara.

"Two in a Million" is described as "a song about falling in love, having somebody to comfort you, and someone to be there for you no matter what." The song sees Jo O'Meara taking lead vocals for the first time. The album version of "Two in a Million" and the Boyfriends & Birthdays version (so named as it was the theme song of their BBC TV movie) are almost exactly the same, except the Boyfriends & Birthdays version has a slightly more robust instrumentation, taking on a more orchestral and R'n'B approach, and pauses the music during the last line of each verse right before the chorus. The latter is included on the North American version of 7. Moreover, the demo version of the song, as heard on "Miami 7", includes loud pop horns in the arrangement, which were removed for album release. However, the horns were re-included in the 2000 version, this time at a lower pitch and a softer volume. The "single version" on the 2003 greatest hits album had different arrangements.

The single includes an exclusive B-side, "We Can Work it Out", which was performed during episode eight of Miami 7, "Alien Hunter". The track is a bubblegum-pop song with distinctively high melodies, and was again co-written by Mike Rose and Nick Foster, who wrote "You're My Number One". The UK release of the single includes the Miami 7 version of "You're My Number One", while the Australian release replaces this with the Jason Nevins remix of "S Club Party". The US release opts for a completely different B-side, containing an exclusive club mix of "Two in a Million" by Mark Penchotti, which has never been released elsewhere.

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