Barons | Titles by Rank
- Barons of Oliveira Castro
- Barons of Oliveira Castro
- Barons of Oliveira do Conde
- Barons of Oliveira Lima
- Barons of Oliveira Roxo
- Barons of Olocau
- Barons of Olonde
- Barons of Oppède
- Barons of Oraison
- Barons of Orchard Portman
- Barons of Orczy de Orczi
- Barons of Ornelas
- Barons of Ortenegg
- Barons of Orval
- Barons of Ossun
- Barons of Oullenbourg-Salbris
- Barons of Ourém
- Barons of Ouricuri
- Barons of Ouro Branco
- Barons of Outre
- Barons of Ovar
- Barons of Overschie
- Barons of Overschie de Neerysche
- Barons of Ovilvar
- Barons of Ow
- Barons of Ow-Wachendorf
- Barons of Oxenstierna
- Barons of Oz
- Barons of Paar de Schönau
- Barons of Paar zu Schönau
- Barons of Pacheco
- Barons of Paço da Figueira
- Barons of Paço de Couceiro
- Barons of Paço de Sousa
- Barons of Paçô Vieira
- Barons of Pagenhardt
- Barons of Paiva
- Barons of Paiva Manso
- Barons of Pajeú
- Barons of Palença
- Barons of Palma
- Barons of Palma
- Barons of Palma
- Barons of Palmares
- Barons of Palme
- Barons of Palmeira
- Barons of Palmeira dos Índios
- Barons of Palmeiras
- Barons of Pandolfina
- Barons of Papelardière