OAO

OAO, a three-letter acronym, may stand for:
 * Orbiting Astronomical Observatory, the name of four NASA scientific satellites
 * Open joint-stock company (Открытое Aкционерное Oбщество), business incorporation in Russia, Ukraine etc.
 * Odessey and Oracle, 1968 album by The Zombies
 * Oddworld: Abe's Oddysee a platform game made by Oddworld Inhabitants released in 1997
 * Over and Out (disambiguation), various meanings including the usual ending of transmissions in telecommunications
 * Open-access operator, a British passenger rail company which does not hold a franchise