Space pirates who raided Enterprise in the Delphic Expanse, stealing supplies and killing a crew member during the search for the Xindi.
The Osaarians are a humanoid species known from their pirate crews operating in the Delphic Expanse. They travel in armed ships and survive by boarding other vessels and taking whatever cargo, equipment and fuel they can carry.
In the episode Anomaly, Osaarian raiders boarded Enterprise soon after it entered the Expanse, stealing much of its antimatter and food stores and killing a crew member. Jonathan Archer captured one of the pirates and, in a dark turn for the captain, threatened him in an airlock to force him to reveal where his comrades were hiding. Enterprise then tracked down the pirate ship, recovered some of the stolen supplies and gathered valuable information about the Expanse.