| Titular See |
Rite/Type |
Bishop |
|
Oasis magna, Oasi maggiore
Oasitan(us)
|
Roman |
|
|
Obba, Obba
Obben(sis)
|
Roman |
|
|
Obbi, Obbi
Obbitan(us)
|
Roman |
 Bishop Adriano Tomasi Travaglia, O.F.M.
|
|
Obori, Obori
Oboritan(us)
|
Roman |
Bishop Juan José Pineda Fasquelle, C.M.F.
|
|
Oca, Oca
Ocoeus
|
Roman |
|
|
Octaba, Ottaba
Octaben(sis)
|
Roman |
Bishop Bernhard Haßlberger
|
|
Octabia, Ottabia
Octabien(sis)
|
Roman |
Bishop Donald Lapointe
|
|
Octava, Ottava
Octaven(sis)
|
Roman |
 Archbishop Blasco Francisco Collaço
|
|
Odessus, Odesso
Odessitan(us)
|
Roman
Archiepiscopal See |
|
|
Oëa, Oea
Oëeb(sis)
|
Roman |
Bishop David Kamau Ng’ang’a
|
|
Oenoanda, Enoanda
Oenoanden(sis)
|
Roman |
|
|
Oescus, Esco
Oescen(sis)
|
Roman |
Bishop Gustavo Garcia-Siller, M.Sp.S.
|
|
Olba, Olba
Olbien(sis)
|
Roman |
|
|
Olbia, Olbia
Olbiatan(us)
|
Roman |
|
|
Olena, Olena
Olenen(sis)
|
Roman |
|
|
Oliva, Oliva
Oliven(sis)
|
Roman |
 Bishop Joseph Martin Sartoris
|
|
Olorun
Oloronen(sis)
|
Roman |
United with Bayonne, France
|
|
Olympus, Olimpo
Olympen(us)
|
Roman |
|
|
Ombi, Ombi
Ombitan(us)
|
Roman |
|
|
Onchesmus, Onchesmo
Onchesmitan(us)
|
Roman |
|
|
Onuphis, Onufi
Onuphitan(us)
Presently: Egypt
|
Roman |
|
|
Opitergium, Oderzo
Opitergin(us)
Presently: Italy
|
Roman |
 Archbishop Alberto Bottari de Castello
|
|
Oppidum Consilinum, Sala Consilina
Consilin(us)
|
Roman |
Bishop Gerard Bernacki
|
|
Oppidum novum, Oppido nuovo
Oppidonoven(sis)
|
Roman |
Bishop Peter Anthony Rosazza
|
|
Opus, Opo
Opuntius
Presently: Greece
|
Roman |
|
|
Orange
Auraiacen(sis)
Presently: France
|
Roman |
|
|
Orcistus, Orcisto
Orcisten(us)
|
Roman |
|
|
Oregon City
Oregonopolitan(us)
Presently: Oregon, United States
|
Roman
Metropolitan See |
 Archbishop Joseph Augustine Di Noia, O.P.
|
|
Oreto
Oretan(us)
Presently: Spain
|
Roman |
|
|
Oreus, Oreo
Orien(sis)
Presently: Greece
|
Roman |
|
|
Orisa, Orisa
Orisen(us)
|
Roman |
|
|
Oropus, Oropo
Oropen(us)
|
Roman |
Suppressed
|
|
Orthosia in Phoenicia, Ortosia di Fenicia
Orthosien(sis) in Phoenicia
|
Roman |
|
|
Orthosias in Caria, Ortosia di Caria
Orthosien(sis) in Caria
|
Roman |
|
|
Orymna, Orimna
Orymnen(sis)
|
Roman |
|
|
Ostra
Ostren(sis)
|
Roman |
Archbishop Francis Assisi Chullikatt
|
|
Ostracine, Ostracine
Ostracinen(sis)
|
Roman |
|
|
Othona
Othonen(sis)
Presently: United Kingdom
|
Roman |
Archbishop George Kocherry
|
|
Otriculum, Otricoli
Otriculan(us)
|
Roman |
Archbishop Tommaso Caputo
|
|
Otrus, Otro
Otroënus
|
Roman |
|
|
Ottana
Othanen(sis)
|
Roman |
Bishop Lorenzo Ghizzoni
|
|
Ottocium, Ottocio
Ottocen(sis)
Presently: Croatia
|
Roman |
Bishop Maurice Paul Delorme, Ist. del Prado
|
|
Oxyrynchus, Ossirinco
Oxyrynchitan(us)
Presently: Egypt
|
Roman
Metropolitan See |
|
