O8

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
 * USS O-8 (SS-69), 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