O11 or O-11 may refer to:
- Curtiss O-11 Falcon, an observation aircraft of the United States Army Air Corps
- HNLMS O 11, a submarine of the Royal Netherlands Navy
- Oxygen-11, an isotope of oxygen
- Stilwell/Cherokee Nation Airport, in Adair County, Oklahoma, United States
- USS O-11 (SS-72), a submarine of the United States Navy
This disambiguation page lists articles associated with the same title formed as a letter–number combination.
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