Osaarians were a humanoid species native to the Alpha Quadrant. The Osaarian people populated an area near the Delphic Expanse. According to the Vulcan database, they owned a large merchant marine fleet in the mid-22nd century; this was one of the very few facts about them known to the Vulcans, as these two species had only met rarely.
An Osaarian merchant ship was encountered by the Enterprise NX-01 in the Expanse in 2153. The vessel raided Enterprise and then led the starship to its first encounter with a Sphere. Enterprise disabled the Osaarian ship and took its Xindi database for use in the search for the Xindi weapon. (ENT: "Anomaly")