Ben Oss is especially craggy on its northern face, falling away steeply to the Cononish glen and barring any direct approach from this direction. It has two main ridges which connect to the adjacent Munros of Ben Lui and Beinn Dubhchraig and walkers usually arrive at the mountains summit along either of these. One ridge goes north east, east and then south east to form a curving edge around Coire Garbh connecting to Beinn Dubhchraig at the Bealach Buidhe with a height of 779 metres. Coire Garbh has Loch Oss lying within its recesses, a body of water measuring roughly 500 by 300 metres. Coire Buidhe stands on the northern side of this eastern ridge, this has a steep headwall and descents north from the bealach to the Cononish glen are not recommended.