Ona or One (sometimes Oøy or Oni) is an island in Øygarden municipality in Hordaland county, Norway. The island lies in the Øygarden archipelago just north of the island of Blomøyna and south of Alvøyna. The Hjeltefjorden lies east of the island and the North Sea and some smaller island lie to the west. The southern portion of the island of Ona is dominated by the Kollsnes natural gas processing facility. The island is low, rocky, and barren, with its highest point being the tall Vareidet hill.