 | O Elvas (Elvas), Portugal |
 | O'Higgins (Rancagua), Chile |
 | Oadby Town (Oadby), England |
| Oak Villa, England |
| Oakdale, England |
| Oakengates Town, England |
| Oakham United, England |
 | Oakland Clippers (Oakland), USA |
| Oakland Stompers (Oakland), USA |
| Oakmere (Liverpool), England |
 | Oakville Blue Devils (Oakville), Canada |
| Oakwood (Crawley), England |
 | Oazis (Yartsevo), Russia |
 | Oberwinter (Remagen), FRG |
 | Obilić (Belgrade), Serbia |
 | Obilić (Belgrade), Serbia and Montenegro |
 | Obilić (Beograd), Yugoslavia |
 | Obod (Tashkent), Uzbekistan |
 | Obolon (Kyiv), Ukraine |
| Obolon (Kyiv), Ukraine |
| Obolon-2 (Kyiv), Ukraine |
| Obolon-Brovar-2 (Bucha), Ukraine |
 | OC Khouribga (Khouribga), Morocco |
 | Ocean Boys (Brass), Nigeria |
 | Ocean View (Zanzibar), Zanzibar |
| Octan (Perm), Russia |
 | Odd (Skien), Norway |
| Odd Down (Bath), England |
 | Oddevold (Uddevalla), Sweden |
| ODEK (Orzhiv), Ukraine |
 | Odense (Odense), Denmark |
| Odense XI (Odense), Denmark |
 | Odisha (Bhubaneswar), India |
 | ODO (Petrozavodsk), USSR |
| ODO (Sverdlovsk), USSR |
| ODO (Tallin), USSR |
| ODO (Tashkent), USSR |
 | Odra (Opole), Poland |
| Odra (Wodzisław Śląski), Poland |
 | Oeste (Itápolis), Brazil |
| Offenburger FV (Offenburg), FRG |
 | OFĪ (Heraklion), Greece |
| OFK (Beograd), Serbia |
| OFK (Beograd), Serbia and Montenegro |
| OFK (Beograd), Yugoslavia |
 | OFK Bar (Bar), Montenegro |
| Ofterdingen (Ofterdingen), FRG |
 | Ogaden Anbassa (Harar), Ethiopia |
| Oggersheim (Ludwigshafen am Rhein), FRG |
| Oguz (Tovuz), USSR |
| Ohetal (Frielendorf), FRG |
| Ok Oltyn (Moskovskyi), USSR |
| Oka (Kolomna), Russia |
| Oka (Kolomna), USSR |
| Okean (Kerch), USSR |
| Okean (Nakhodka), Russia |
| Okean (Nakhodka), USSR |
| Okean (Vladivostok), USSR |
| Okean-D (Nakhodka), Russia |
| Okehampton Argyle (Okehampton), England |
 | Okoume FC, Gabon |
 | Okwahu United (Nkawkaw), Ghana |
 | Okzhetpes (Kokshetau), Kazakhstan |
 | Olaine (Olaine), Latvia |
 | Olancho (Juticalpa), Honduras |
| Olaria (Rio de Janeiro), Brazil |
 | Old Benedictans (Colombo), Sri Lanka |
| Old Brightonians, England |
| Old Carthusians (Godalming), England |
| Old Castle Swifts, England |
| Old Cranleighans, England |
 | Old Edwardians (Freetown), Sierra Leone |
| Old Etonians (Eton), England |
| Old Foresters (Walthamstow), England |
| Old Grammarians (Ipswich), England |
| Old Harrovians (Harrow), England |
| Old Hill Wanderers, England |
| Old Hullensians, England |
| Old Johnians, England |
| Old Kingstonians, England |
| Old Lyonian, England |
| Old Philberdians, England |
| Old Salopians, England |
| Old St Mark's, England |
| Old St Paul's, England |
| Old St Stephens, England |
| Old Westminsters (London), England |
| Old Whittington Mutuals, England |
| Old Woodstock Town (Woodstock), England |
| Old Wykehamists (Winchester), England |
| Old Xaverians, England |
| Oldbury Town, England |
| Oldbury United (Oldbury), England |
| Oldenburg (Oldenburg), FRG |
| Oldenburg (Oldenburg 1894), FRG |
| Oldfields, England |
| Oldham Athletic (Oldham), England |
| Oldham Boro (Oldham), England |
| Oldham County (Oldham), England |
| Oldland Abbotonians (Oldland Common), England |
| Olhanense (Olhao), Portugal |
| Olimp (Fryazino), USSR |
| Olimp (Khimki), Russia |
| Olimp-Dolgoprudny (Dolgoprudny), Russia |
| Olimp-Dolgoprudny-2 (Dolgoprudny), Russia |
 | Olimpia (Asunción), Paraguay |
| Olimpia (Ljubljana), Yugoslavia |
| Olímpia (Olímpia), Brazil |
| Olimpia (Poznań), Poland |
| Olimpia (Rīga), Latvia |
| Olimpia (Tegucigalpa), Honduras |
 | Olimpic (Sarajevo), Bosnia and Herzegovina |
| Olímpico (Blumenau), Brazil |
| Olímpico (Manaus), Brazil |
| Olímpico Pirambu Futebol Clube (Pirambu), Brazil |
 | Olimpija (Ljubljana), Slovenia |
| Olimpija (Ljubljana), Slovenia |
| Olimpik (Tashkent), Uzbekistan |
 | Olimpik (Teteven), Bulgaria |
| Olimpiya (Alma-Ata), USSR |
| Olimpiya (Artashat), USSR |
| Olimpiya (Gelendzhik), Russia |
| Olimpiya (Kirovo-Chepetsk), Russia |
| Olimpiya (Savyntsi), Ukraine |
| Olimpiya (Volgograd), Russia |
 | Olimpo (Bahía Blanca), Argentina |
| Olimps (Rīga), Latvia |
| Oliveirense (Oliveira de Azemeis), Portugal |
| Olkom (Melitopol), Ukraine |
| Ollerton Colliery, England |
 | Olmedo (Riobamba), Ecuador |
| Olney Town, England |
| Olympia (Bocholt), FRG |
 | Olympia (Bruxelles), Belgium |
| Olympia (Germaringen), FRG |
 | Olympia (Wien), Austria |
| Olympia (Wilhelmshaven), FRG |
| Olympia Kirrlach (Waghäusel), FRG |
| Olympia Neugablonz (Kaufbeuren), FRG |
 | Olympiakos (Nicosia), Cyprus |
| Olympiakós (Pireus), Greece |
| Olympiakos Volos (Volos), Greece |
| Olympian, England |
| Olympic, England |
| Olympic (Charleroi), Belgium |
 | Olympic FC (Niamey), Niger |
 | Olympic Real (Bangui), Central African Republic |
| Olympik (Donetsk), Ukraine |
| Olympik (Kharkiv), Ukraine |
| Olympik (Kirovohrad), Ukraine |
 | Olympique (Bamako), Mali |
 | Olympique (Le Marin), Martinique |
 | Olympique (Morne-à-l'Eau), Guadeloupe |
 | Olympique de Béja (Béja), Tunisia |
| Olympique de Casablanca (Casablanca), Morocco |
 | Olympique de Cayenne (Cayenne), Guyana |
 | Olympique de Missiri (Missiri), Comoros |
 | Olympique de Moka (Moka), Mauritius |
 | Olympique de Ngor (Dakar), Senegal |
| Olympique des Transports (Tunis), Tunisia |
 | Olympique Kakandé (Boké), Guinea |
 | Olympique Lillois (Lille), France |
 | Olympique Mvolyé (Yaoundé), Cameroon |
| Olympique Sportif (Libreville), Gabon |
 | Olympique Star, Burundi |
| Olympischer (Bremerhaven), FRG |
 | Omagh Town (Omagh), Northern Ireland |
| Omai Gold Seekers (Georgetown), Guyana |
 | Oman (Muscat), Oman |
| Omedla (Addis Abeba), Ethiopia |
| Omonia (Nicosia), Cyprus |
 | Once Caldas (Manizales), Colombia |
 | Once Deportivo (Ahuachapan), El Salvador |
| Once Lobos (Chalchuapa), El Salvador |
| Once Municipal (Ahuachapan), El Salvador |
| Onze Créateurs (Bamako), Mali |
| Oostende (Ostend), Belgium |
| Oostendensche (Ostende), Belgium |
 | Opava (Opava), Czech Republic |
| Opel (Rüsselsheim), FRG |
| Operário (Campo Grande), Brazil |
| Operário (Várzea Grande), Brazil |
| Operário Ferroviário (Ponta Grossa), Brazil |
| Oppau (Ludwigshafen am Rhein), FRG |
| Oqtepa (Tashkent), Uzbekistan |
 | Orapa United (Orapa), Botswana |
| Orašje (Orašje), Bosnia and Herzegovina |
| Oratório (Macapá), Brazil |
| Orbita (Belaya Kalitva), USSR |
 | Orbita (Minsk), Belarus |
| Orbita (Zaporizhzhya), Ukraine |
| Ordabasy (Shymkent), Kazakhstan |
| Ordabasy-2 (Shymkent), Kazakhstan |
 | Orduspor (Ordu), Turkey |
| Ordzhonikidze Factory (Leningrad), USSR |
| Örebro (Örebro), Sweden |
| Orel-Chegan 30 (Vratsa), Bulgaria |
| Oresa (Lyuban), Belarus |
| Oreston Rovers, England |
| Orgenergostroy (Dimitrovgrad), Russia |
| Örgryte (Göteborg), Sweden |
| Oriental (Lisboa), Portugal |
 | Oriente Petrolero (Santa Cruz de la Sierra), Bolivia |
 | Orijent (Rijeka), Croatia |
| Orlando City (Orlando), USA |
 | Orlando Pirates (Johannesburg), South Africa |
| Orlovets (Gabrovo), Bulgaria |
| Ormskirk, England |
| Ormskirk, England |
 | Oro (Guadalajara), Mexico |
| Orpington, England |
| Orrell, England |
| Orwell Works, England |
| Oryx Douala (Douala), Cameroon |
| Os (Os), Norway |
 | Os Balantas (Mansôa), Guinea-Bissau |
| Osberton Radiator, England |
| Osborne Athletic, England |
| OSDYuSSHOR Zhas Ulan (Shymkent), Kazakhstan |
 | Oserian Fastac FC (Naivasha), Kenya |
| Osijek (Osijek), Croatia |
| Osijek (Osijek), Yugoslavia |
| Oskil (Kupyansk), Ukraine |
| Oslebshausen (Bremen), FRG |
| Osmanlıspor (Ankara), Turkey |
| Osnabrück (Osnabrück), FRG |
| Osnova (Vichuga), USSR |
 | Osotspa (Saraburi), Thailand |
 | Oss (Oss), Netherlands |
| Ossett Albion (Ossett), England |
| Ossett Town (Ossett), England |
| Ossett United (Ossett), England |
| OSShIOSD (Taraz), Kazakhstan |
| Ostbahn XI (Wien), Austria |
| Osterholz-Tenever (Bremen), FRG |
| Östers (Växjö), Sweden |
| Östersunds (Östersund), Sweden |
| Östringen (Östringen), FRG |
| OSV Hannover (Hannover), FRG |
| Oswaldtwistle Rovers, England |
| Oswestry Town (Oswestry), England |
 | Oţelul (Galaţi), Romania |
 | Otôho (Oyo), Congo |
| Otrant (Ulcinj), Montenegro |
| Ottawa Fury (Ottawa), Canada |
| Ottering (Moosthenning), FRG |
| Ottery St Mary, England |
| Ottfingen (Wenden), FRG |
| Ottobrunn (Ottobrunn), FRG |
| Ottweiler (Ottweiler), FRG |
| Ouakam (Dakar), Senegal |
| Oud-Heverlee (Leuven), Belgium |
 | Oulu (Oulu), Finland |
| Our Company (Astana), Kazakhstan |
| Ouston Rovers, England |
| Ouston United, England |
| Overseal Swifts, England |
| Owlerton, England |
| Owston Park Rangers, England |
| Oxford City (Marston), England |
| Oxford Cygnets, England |
| Oxford United (Oxford), England |
| Oxford University (Oxford), England |
| Oxhey Jets (South Oxhey), England |
