"O" is the title of the debut single from R&B singer Omarion and the first from his album of the same name, O.

The single was a top 30 hit in the U.S., peaking at #27. "O" was also the first choice for Omarion's debut single in the UK and was picked over "Touch", which was the original first choice of UK single. The song peaked at #47 and spent two weeks within the top 75 of the UK singles chart.