O8 or O-8 may refer to:
Douglas O-8, an airplane Oasis Hong Kong Airlines, a defunct Hong Kong airline Octaoxygen (O8) an allotrope of oxygen Omaha/8, a poker variant Siam Air, a defunct Thai airline , a O-class submarine of the United States Navy O-8, a pay grade of the uniformed services of the United States HMS H6, also known in the Royal Netherlands Navy as HNLMS O 8
See also 08 (disambiguation) 8O (disambiguation)