| Living Prelates (Total 5656) * |
  Archbishop Patrick Michael O’Regan (67), Metropolitan Archbishop of Adelaide (Australia) |
  Bishop Colm O’Reilly (91), Bishop emeritus of Ardagh (Ireland) |
| Archbishop Kieran O’Reilly, S.M.A. (73), Metropolitan Archbishop of Cashel and Emly (Ireland) |
| Bishop Philip Leo O’Reilly (82), Bishop emeritus of Kilmore (Ireland) |
 Archbishop Mark O’Toole (62), Metropolitan Archbishop of Cardiff–Menevia (Wales) |
  Bishop David James Oakley (70), Bishop of Northampton (England) |
 Bishop John Oballa Owaa (67), Bishop of Ngong (Kenya) |
  Archbishop Ildefonso Obama Obono (87), Metropolitan Archbishop emeritus of Malabo (Equatorial Guinea) |
| Bishop Joseph Obanyi Sagwe (58), Bishop of Kakamega (Kenya) |
 Archbishop Emmanuel Obbo, A.J. (73), Metropolitan Archbishop of Tororo (Uganda) and Apostolic Administrator of Jinja (Uganda) |
 Archbishop Anthony John Valentine Obinna (79), Metropolitan Archbishop emeritus of Owerri (Nigeria) |
 Bishop Ernest Anaezichukwu Obodo (59), Titular Bishop of Mediana, Apostolic Administrator of Abakaliki (Nigeria) and Auxiliary Bishop of Enugu (Nigeria) |
 Bishop Celestino Ocampo Gaona (64), Bishop of Carapeguá (Paraguay) |
 Bishop Joel Ocampo Gorostieta (62), Bishop of Zamora (Mexico) |
 Bishop Luisito Audal Occiano (54), Bishop of Virac (Philippines) |
 Bishop Marek Ochlak, O.M.I. (60), Bishop of Fenoarivo Atsinanana (Madagascar) |
 Bishop Armando Xavier Ochoa (83), Bishop emeritus of Fresno (USA) |
 Bishop Manuel Ochogavía Barahona, O.S.A. (58), Bishop of Colón–Kuna Yala (Panama) and General Secretary of Episcopal Conference of Panama |
| Archbishop John Baptist Odama (78), Metropolitan Archbishop emeritus of Gulu (Uganda) |
 Bishop Sławomir Oder (65), Bishop of Gliwice (Poland) |
| Bishop Peter Kayode Odetoyinbo (62), Bishop of Abeokuta (Nigeria) |
| Bishop Sabino Ocan Odoki (68), Bishop of Arua (Uganda) |
| Bishop Henry Juma Odonya (49), Bishop of Kitale (Kenya) |
| Bishop Vincent Ouma Odundo (47), Titular Bishop of Giru Marcelli and Auxiliary Bishop of Kisumu (Kenya) |
 Bishop Euzébius Chinekezy Ogbonna Managwu (66), Bishop of Port-Gentil (Gabon) |
 Bishop Óscar Vicente Ojea Quintana (79), Bishop emeritus of San Isidro (Argentina) |
| Bishop Crispin Ojeda Márquez (74), Bishop of Tehuantepec (Mexico) |
 Archbishop Simon Ok Hyun-jjn (옥현진 시몬 / 玉賢進) (58), Metropolitan Archbishop of Gwangju 광주 (South Korea) and General Secretary of Catholic Bishops’ Conference of Korea |
| Bishop Hilary Paul Odili Okeke (79), Bishop emeritus of Nnewi (Nigeria) |
| Archbishop Valerian Maduka Okeke (72), Metropolitan Archbishop of Onitsha (Nigeria) |
 Cardinal Anthony Olubunmi Okogie (89), Cardinal-Priest of S. Maria del Monte Carmelo a Mostacciano, Metropolitan Archbishop emeritus of Lagos (Nigeria) and former Member of Council of Cardinals for the Study of Organisational and Economic Problems of the Apostolic See |
| Archbishop Jude Thaddeus Okolo (69), Titular Archbishop of Novica and Apostolic Nuncio to Haiti |
| Bishop Emmanuel Okombo Wandera (83), Bishop emeritus of Kericho (Kenya) |
| Bishop Michael Nnachi Okoro (85), Bishop emeritus of Abakaliki (Nigeria) |
| Archbishop Zacchaeus Okoth (83), Metropolitan Archbishop emeritus of Kisumu (Kenya) |
| Bishop John Ifeanyichukwu Okoye (75), Bishop of Awgu (Nigeria) |
| Bishop Jonas Benson Okoye (63), Bishop of Nnewi (Nigeria) |
 Cardinal Peter Ebere Okpaleke (63), Cardinal-Priest of Ss. Martiri dell’Uganda a Poggio Ameno and Bishop of Ekwulobia (Nigeria) |
| Bishop Arkadiusz Okroj (58), Bishop of Toruń (Poland) |
 Bishop Orlando Olave Villanoba (57), Bishop of Ocaña (Colombia) |
 Archbishop Miguel Angel Olaverri Arroniz, S.D.B. (77), Metropolitan Archbishop emeritus of Pointe-Noire (Congo-Brazzaville) |
 Bishop Francesco Oliva (75), Bishop of Locri–Gerace (Italy) |
 Bishop Ivanildo Oliveira Almeida (54), Bishop of Cametá (Brazil) |
| Archbishop Walmor Oliveira de Azevedo (71), Metropolitan Archbishop of Belo Horizonte (Brazil) and Ordinary of Ordinariato para os Fiéis de Ritos Orientais no Brasil of the Eastern Rite (Brazil) |
| Bishop José Geraldo Oliveira do Valle, C.S.S. (96), Bishop emeritus of Guaxupé (Brazil) |
| Bishop José Otacio Oliveira Guedes (52), Titular Bishop of Severiana and Auxiliary Bishop of Belo Horizonte (Brazil) |
 Bishop Juan Bautista Tomás Oliver Climent, O.F.M. (74), Titular Bishop of Legis Volumni and Vicar Apostolic emeritus of Requena (Peru) |
| Archbishop João Bosco Óliver de Faria (86), Metropolitan Archbishop emeritus of Diamantina (Brazil) |
 Bishop Victorio Oliver Domingo (96), Bishop emeritus of Orihuela–Alicante (Spain) |
| Bishop Santiago Olivera (67), Military Ordinary of Argentina (Argentina) |
| Bishop Mario Oliveri (82), Bishop emeritus of Albenga–Imperia (Italy) |
| Bishop Donato Oliverio (70), Bishop of Lungro of the Italo-Albanese (Italy) |
| Bishop Derio Olivero (65), Bishop of Pinerolo (Italy) |
 Bishop Paulinus Yan Olla, M.S.F. (62), Bishop of Tanjung Selor (Indonesia) |
| Bishop Pedro María Olmedo Rivero, C.M.F. (81), Bishop-Prelate emeritus of Humahuaca (Argentina) |
| Bishop Thomas James Olmsted (79), Bishop emeritus of Phoenix (USA) |
| Bishop Martin Dada Abejide Olorunmolu (77), Bishop of Lokoja (Nigeria) |
| Bishop Michael Fors Olson (59), Bishop of Fort Worth (USA) |
| Bishop Grzegorz Olszowski (59), Titular Bishop of Rhoga and Auxiliary Bishop of Katowice (Poland) |
| Cardinal Juan José Omella Omella (79), Cardinal-Priest of S. Croce in Gerusalemme, Metropolitan Archbishop of Barcelona (Spain) and Member of Council of Cardinals |
| Bishop Callistus Valentine Chukwuma Onaga (67), Bishop of Enugu (Nigeria) |
| Bishop Godfrey Igwebuike Onah (69), Bishop of Nsukka (Nigeria) |
| Cardinal John Olorunfemi Onaiyekan (82), Cardinal-Priest of S. Saturnino and Metropolitan Archbishop emeritus of Abuja (Nigeria) |
| Bishop Jean-Vincent Ondo Eyene (66), Bishop of Oyem (Gabon) and President of Episcopal Conference of Gabon |
| Bishop Honesto Flores Ongtioco (77), Bishop emeritus of Cubao (Philippines) |
 Bishop Gonzalo Alfredo Ontiveros Vivas (57), Vicar Apostolic of Caroní (Venezuela) |
 Bishop John Opoku-Agyemang (68), Bishop of Konongo–Mampong (Ghana) |
| Bishop Radosław Orchowicz (56), Titular Bishop of Surista and Auxiliary Bishop of Gniezno (Poland) |
 Bishop Ángel Maximiliano Ordoñez Sigcho (54), Titular Bishop of Phelbes and Auxiliary Bishop of Quito (Ecuador) |
| Bishop Edson José Oriolo dos Santos (61), Bishop of Leopoldina (Brazil) |
| Bishop Giuseppe Orlandoni (87), Bishop emeritus of Senigallia (Italy) |
 Bishop José Ornelas Carvalho, S.C.I. (72), Bishop of Leiria–Fátima (Portugal) and President of Episcopal Conference of Portugal |
| Bishop Vincenzo Carmine Orofino (72), Bishop of Tursi–Lagonegro (Italy) |
 Bishop Domingo Oropesa Lorente (75), Bishop of Cienfuegos (Cuba) |
 Archbishop Ján Orosch (72), Archbishop of Trnava (Slovakia) |
 Bishop Atanáz Orosz (65), Bishop of Miskolc of the Hungarians (Hungary) |
| Bishop Francisco Jesús Orozco Mengíbar (55), Bishop of Guadix (Spain) |
| Bishop Guillermo Orozco Montoya (79), Bishop emeritus of Girardota (Colombia) |
| Bishop César Alfonso Ortega Díaz (56), Bishop of Linares (Mexico) |
| Archbishop Alberto Ortega Martín (63), Titular Archbishop of Midila and Apostolic Nuncio to Venezuela |
| Bishop Fernando Ortega Ortega (52), Titular Bishop of Thizica and Auxiliary Bishop of Cuenca (Ecuador) |
| Bishop José María Ortega Trinidad (75), Bishop-Prelate emeritus of Juli (Peru) |
| Bishop Armando António Ortíz Aguirre (74), Bishop of Ciudad Lázaro Cárdenas (Mexico) |
| Bishop Joseph Osei-Bonsu (78), Bishop emeritus of Konongo–Mampong (Ghana) |
| Bishop Cleophas Oseso Tuka (58), Bishop of Nakuru (Kenya) |
 Bishop Berard Toshio Oshikawa (ベラルド 押川壽夫), O.F.M. Conv. (85), Bishop emeritus of Naha 那覇 (Japan) |
| Bishop Wojciech Tomasz Osial (55), Bishop of Łowicz (Poland) |
 Bishop Thomas Osman, O.F.M. Cap. (75), Bishop of Barentu of the Eritreans (Eritrea) |
| Cardinal Carlos Osoro Sierra (80), Cardinal-Priest of S. Maria in Trastevere, Metropolitan Archbishop emeritus of Madrid (Spain) and Ordinary emeritus of Spain of the Eastern Rite (Spain) |
| Bishop José Roberto Ospina Leongómez (79), Apostolic Administrator of the Military Ordinariate of Colombia (Colombia) and Bishop emeritus of Buga (Colombia) |
| Archbishop Jorge Alberto Ossa Soto (69), Metropolitan Archbishop of Nueva Pamplona (Colombia) |
 Bishop Pedro Mario Ossandón Buljevic (68), Military Ordinary of Chile (Chile) |
 Bishop Cajetan Francis Osta (64), Bishop of Muzaffarpur (India) |
 Bishop Stefan Oster, S.D.B. (60), Bishop of Passau (Germany) |
| Bishop Janusz Ostrowski (61), Titular Bishop of Caltadria and Auxiliary Bishop of Warmia (Poland) |
| Bishop Michael Otieno Odiwa (63), Bishop of Homa Bay (Kenya) |
| Bishop Paul Yoshinao Otsuka (パウロ 大塚喜直) (71), Bishop of Kyoto 京都 (Japan) |
| Archbishop Giacomo Guido Ottonello (79), Titular Archbishop of Sasabe |
 Bishop Joseph John Oudeman, O.F.M. Cap. (84), Titular Bishop of Respecta and Auxiliary Bishop emeritus of Brisbane (Australia) |
 Bishop Ambroise Ouédraogo (77), Bishop emeritus of Maradi (Niger) |
