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- Obazine Abbey (also Aubazine Abbey), monks, diocese of Limoges (Aubazine, Corrèze)
- Oelenberg Abbey (Abbaye Notre-Dame d'Oelenberg), monks (Reiningue, Haut-Rhin)
- L'Olive Abbey (also known as L'Hermitage Abbey), nuns, diocese of Cambrai
- Les Olives Abbey (also Les Olieux Abbey), nuns, diocese of Narbonne
- Olivet Abbey (Abbaye Notre-Dame d'Olivet), monks, diocese of Bourges (Saint-Julien-sur-Cher, Cher
- Ounans Abbey (Abbaye Notre-Dame d'Ounans), nuns, diocese of Besançon (Ounans, Jura)
- Ourscamp Abbey (Abbaye Notre-Dame d'Ourscamp), monks, diocese of Noyon (Chiry-Ourscamp, Oise)
Read more about this topic: List Of Cistercian Monasteries In France