O11

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