Seil is separated from mainland Scotland by the Clachan Sound, which is only about at its narrowest point. To the west lies the sea-lane of the Firth of Lorn. The island of Luing lies across the Cuan Sound to the south and beyond are Lunga and Scarba. Smaller islands surrounidng Seil are its companion Slate Islands of Easdale, Torsa, Belnahua and Shuna. Eilean Dubh Mòr is to the south-west with the Garvellachs beyond, with Insh to the north west.