Search by letter: O
Search by letter
Search by letter: O
- Oil refinery (petroleum refinery) Oil refinery
- Oil refining
- Oil sands (tar sands): composition, extraction, impacts, and global significance Oil sands
- Oil spill: causes, impacts, response, and prevention Oil spill
- Oil tanker: design, types, history, operations and environmental impact Oil tanker
- Oil well: purpose, types, drilling methods and operational roles Oil well
- Oilton, Oklahoma
- Oiniades (municipal unit in Aetolia-Acarnania, Greece) Oiniades
- Oinikhol Bobonazarova
- Oiran: high-ranking courtesans of Japan’s Edo era Oiran
- Oireachtas — Ireland's National Legislature Oireachtas
- Oise — department in Hauts-de-France, northern France Oise
- Ōiso: coastal town in Kanagawa Prefecture, Japan Ōiso
- Oisseau — commune in Mayenne, Pays de la Loire, France Oisseau
- Oisseau-le-Petit — commune in Sarthe, Pays de la Loire Oisseau-le-Petit
- Oisy-le-Verger
- Oisy, Aisne — commune in northern France Oisy, Aisne
- Ōita (city) — capital of Ōita Prefecture, Japan Ōita (city)
- Ōita Prefecture — Onsen region of northeastern Kyūshū, Japan Ōita Prefecture
- Oita Trinita
- Oiva Toikka — Finnish glass designer and creator of the Iittala Birds Oiva Toikka
- Oizé — commune in Sarthe, Pays de la Loire, France Oizé
- Ojai, California: valley town of arts, nature, and retreat Ojai, California
- Ojibwe (Anishinaabe people of Canada and the United States) Ojibwe
- Ōjin Seamount: Extinct Guyot in the Hawaiian–Emperor Seamount Chain Ōjin Seamount
- Ojo, Lagos State: town and local government area Ojo
- Ojo Maduekwe
- Ojos del Salado: Highest Active Volcano and Second-Highest Peak in the Americas Ojos del Salado
- OK — meaning, origins, uses, and variations OK
- OK Computer — Radiohead album (1997) OK Computer
- OK Go
- Okaloosa County, Florida
- Ōkami (video game) Ōkami
- Okan Buruk — Turkish football player and manager Okan Buruk
- Okanagan Valley: geography, culture, economy and notable features Okanagan
- Okanagan Lake
- Okanogan County, Washington
- Okanogan, Washington — city and county seat in north‑central Washington Okanogan, Washington
- Okapi (Okapia johnstoni) — Central African forest giraffid Okapi
- Okara District (Pakistan) Okara District
- Okara Tehsil, Punjab, Pakistan Okara Tehsil
- Okara, Pakistan: city and district capital in Punjab Okara, Pakistan
- Okay, Oklahoma
- Okayama — capital city of Okayama Prefecture, Japan Okayama
- Okayama Castle — the 'Crow Castle' of Okayama Okayama Castle
- Okayama Prefectural Museum — regional history and cultural collections Okayama Prefectural Museum
- Okayama Prefecture: geography, history, culture and attractions Okayama Prefecture
- Okayama — capital city of Okayama Prefecture, Japan Okayama, Okayama
- Okazaki, Aichi — city in central Japan Okazaki, Aichi
- Okeanids (Oceanids): water nymphs of Okeanos and Tethys Okeanid
- Okeanos (Oceanus) — Titan and personification of the encircling river Okeanos
- Okeechobee County, Florida
- Okeechobee, Florida
- Okeene, Oklahoma: A small town in Blaine County Okeene, Oklahoma
- Okefenokee Swamp — a blackwater peatland on the Georgia–Florida border Okefenokee Swamp
- Okehampton: Market Town Gateway to Dartmoor Okehampton
- Okemah, Oklahoma — county seat and birthplace of Woody Guthrie Okemah, Oklahoma
- Okfuskee County, Oklahoma
- Oki Airport (隠岐空港) — regional airport on Dōgo, Oki Islands Oki Airport
- Oki Province (Oki no kuni): an island province of Japan Oki Province
- Okiharu Yasuoka (1939–2019) — Japanese lawyer and politician Okiharu Yasuoka
- Okinawa: geography, history, culture, and natural heritage Okinawa
- Okinawa (city): overview, history, culture and transport Okinawa (city)
- Okinawa Prefecture
- Okinawa Urban Monorail (Yui Rail) Okinawa Urban Monorail
- Okinawan language (Uchināguchi) Okinawan language
- Okinotorishima
- Oklahoma: geography, history, economy, and culture Oklahoma
- Oklahoma City
- Oklahoma City Barons — American Hockey League team and Edmonton Oilers affiliate Oklahoma City Barons
- Oklahoma City Blue
- Oklahoma City bombing (April 19, 1995) Oklahoma City bombing
- Oklahoma City Thunder
- Oklahoma County, Oklahoma — overview, history, and key facts Oklahoma County, Oklahoma
- Oklahoma House of Representatives
- Oklahoma Land Run (Land Rush of 1889) Oklahoma Land Run
- Oklahoma Panhandle
- Oklahoma Rose: the hybrid tea rose of Oklahoma Oklahoma Rose
- Oklahoma Senate
- Oklahoma State University
- Oklahoma Territory (1890–1907) Oklahoma Territory
- Oklahoma! — landmark 1943 Rodgers and Hammerstein musical Oklahoma! (musical)
- Oklahoma! (song)
- Okmulgee County, Oklahoma: overview, history, and features Okmulgee County, Oklahoma
- Okmulgee, Oklahoma — county seat and Muscogee (Creek) Nation center Okmulgee, Oklahoma
- Okoboji, Iowa: Lakefront City in the Iowa Great Lakes Region Okoboji, Iowa
- Okolona, Mississippi — small city and county seat in Chickasaw County Okolona, Mississippi
- Okonomiyaki — Japanese savory pancake and regional styles Okonomiyaki
- Okra (Abelmoschus esculentus): description, cultivation, culinary and cultural uses Okra
- Okroshka: Cold Russian Soup of Kvass, Vegetables and Eggs Okroshka
- Oksana Baiul — Ukrainian Olympic and World Champion Figure Skater Oksana Baiul
- Oksana Grishuk — Russian Olympic Champion Ice Dancer Oksana Grishuk
- Oksana Shachko: Ukrainian artist and FEMEN co‑founder Oksana Shachko
- Oktaha, Oklahoma
- Oktibbeha County, Mississippi: Starkville and the University-Centered Community Oktibbeha County, Mississippi
- Oktoberfest (Wiesn): Munich's annual beer and folk festival Oktoberfest
- Ōkuma, Fukushima
- Okutama, Tokyo: Mountain town, reservoir, and outdoor gateway Okutama, Tokyo
- Okwui Enwezor: Curator, Critic, and Global Art Intellectual Okwui Enwezor
- Ol Doinyo Lengai: Tanzania’s unique carbonatite volcano Ol Doinyo Lengai
- Ol' Dirty Bastard (Russell Tyrone Jones) Ol' Dirty Bastard
- Ola L. Mize
- Ola Magnell
- Ola Mildred Rexroat — Oglala Sioux pilot and air traffic controller Ola Mildred Rexroat
- Ola Ullsten: Swedish Liberal Leader and Prime Minister (1931–2018) Ola Ullsten
- Ola, Arkansas: small city in Yell County and local community hub Ola, Arkansas
- Olaf Kölzig: South African‑born German NHL Goaltender and Career Overview Olaf Kölzig
- Olaf Marschall — German footballer and forward (born 1966) Olaf Marschall
- Olaf Pooley (1914–2015) — English actor and screenwriter Olaf Pooley
- Olaf Scholz — German politician and Chancellor of Germany Olaf Scholz
- Olaf Thon — German footballer and midfielder Olaf Thon
- Olaf Tryggvason (c. 968–1000) — Viking leader and King of Norway Olaf Tryggvason
- Ólafur Ragnar Grímsson
- Olaine — town in Latvia Olaine
- Öland — Swedish island in the Baltic Sea Öland
- Öland Bridge (Ölandsbron) Öland Bridge
- Öland County (1819–1826) — former Swedish county Öland County
- Olanzapine (Zyprexa): an atypical antipsychotic used for schizophrenia and bipolar disorder Olanzapine
- Olathe, Kansas
- Olaudah Equiano (Gustavus Vassa): Life, Writings, and Abolitionist Influence Olaudah Equiano
- Olav Skjevesland — Norwegian theologian and bishop Olav Skjevesland
- Olavi Lanu — Finnish sculptor and creator of naturalistic public works (1925–2015) Olavi Lanu
- Olavi Mäenpää: Finnish politician and leader of Suomen Kansan Sinivalkoiset Olavi Mäenpää
- Olavi Mannonen — Finnish modern pentathlete and police officer Olavi Mannonen
- Olavo Rodrigues Barbosa (Nena) — Brazilian footballer Olavo Rodrigues Barbosa
- Olbia, Sardinia Olbia
- Old age
- Old Believers (Russian Orthodox schism and tradition) Old Believers
- Old Bridge Township, New Jersey
- Old Brownsboro Place, Kentucky
- Old Calendarists (Eastern Orthodox traditionalists) Old Calendarists
- Old Catholic Church
- Old Chicago Main Post Office Redevelopment (proposed project) Old Chicago Main Post Office Redevelopment
- Old Christian Cemetery, Abbottabad Old Christian Cemetery Abbottabad
- Old Church Slavonic: Early Slavic Literary and Liturgical Language Old Church Slavonic
- Old City of Jerusalem Old City (Jerusalem)
- Old College, University of Edinburgh
- Old Corral, California — unincorporated community in Madera County Old Corral, California
- Old Delhi (Shahjahanabad): history, landmarks, and cultural life Old Delhi
- Old Dominion University
- Old Earth creationism
- Old English (Anglo-Saxon): history, structure and literary legacy Old English
- Old Faithful Geyser
- Old Firm: Celtic and Rangers rivalry in Scottish football Old Firm
- Old Ford, East London Old Ford
- Old Forge, Lackawanna County, Pennsylvania
- Old French (langue d'oïl): early Romance language of northern France Old French
- Old Frisian: a medieval West Germanic language Old Frisian
- Old Greenwich, Connecticut — neighborhood and coastal village Old Greenwich, Connecticut
- Old Harbor, Alaska — coastal community on Kodiak Island Old Harbor, Alaska
- Old Japanese: the language of early Nara and its written record Old Japanese
- Old Kingdom of Egypt: Age of the Pyramids and Early Centralized State Old Kingdom of Egypt
- Old MacDonald Had a Farm — children's song, structure, history and uses Old MacDonald Had a Farm
- Old Major (Animal Farm)
- Old master print
- Old Melbourne Gaol — history, design, notable events and museum Old Melbourne Gaol
- Old Money (The Simpsons episode) Old Money
- Old New Borrowed and Blue — Slade (1974 album) Old New Borrowed and Blue
- Old Norse: language of the Viking Age Old Norse language
- Old North Church (Christ Church in the City of Boston) Old North Church
- Old Persian: Early Southwestern Iranian Language and Achaemenid Inscriptions Old Persian language
- Old Possum's Book of Practical Cats
- Old Prussian language
- Old Red Sandstone
- Old River‑Winfree, Texas Old River-Winfree, Texas
- Old Saybrook, Connecticut
- Old School (2003 film) Old School (movie)
- Old St Paul’s Cathedral — the medieval cathedral of the City of London Old St Paul's Cathedral
- Old Street station — Central London Underground and National Rail interchange Old Street station
- Old Style and New Style dates: Julian vs Gregorian and the change of the new year Old Style and New Style dates
- Old Synagogue (Erfurt) — medieval Jewish site and museum Old Synagogue (Erfurt)
- Old Testament (Hebrew Bible): Overview, Structure, History, and Canonical Differences Old Testament
- Old Tom Morris: Scottish golf pioneer and St Andrews greenskeeper Old Tom Morris
- Old Town (historic urban centre) Old town
- Old Town Road — Lil Nas X song, remixes, charts and cultural impact Old Town Road
- Old Town, Chicago
- Old Trafford — Manchester United's stadium, the 'Theatre of Dreams' Old Trafford
- Old World (Europe, Asia and Africa): historical and geographic overview Old World
- Old World Flycatchers (family Muscicapidae) Old World flycatcher
- Old World monkeys (Cercopithecidae): diversity, behaviour and conservation Old World monkey
- Old World Underground, Where Are You Now? (Metric album) Old World Underground, Where Are You Now?
- Old World vulture
- Old World warbler
- Old Yeller
- Old Yeller (1957 film) Old Yeller (movie)
- Old-growth forest
- Old-school hip hop: the early recorded era of hip hop culture Old-school hip hop
- Oldambt
- Oldebroek, Gelderland — Dutch municipality Oldebroek
- Oldenborstel (municipality in Schleswig-Holstein) Oldenborstel
- Oldenburg (city in Lower Saxony, Germany) Oldenburg (city)
- Oldenburg (district), Lower Saxony Oldenburg (district)
- Oldenzaal: Historic City and Municipality in Overijssel, Netherlands Oldenzaal
- Oldest dated rocks and minerals on Earth and the Moon Oldest dated rocks
- Oldest people (verified longevity records) Oldest people
- Oldfield Thomas (1858–1929) — British mammalogist Oldfield Thomas
- Oldham — town in Greater Manchester, England Oldham
- Oldham Athletic A.F.C.
- Oldham County, Kentucky — overview, history, and communities Oldham County, Kentucky
- Oldham County, Texas — overview, geography, history, and uses Oldham County, Texas
- Oldham Cricket Club
- Olds, Iowa — small Midwestern community Olds, Iowa
- Oldsmar, Florida
- Oldsmobile: American automobile marque Oldsmobile
- Oldsmobile Cutlass
- Oldtown, Idaho
- Olduvai Gorge: Key site for early human history in East Africa Olduvai Gorge
- Ole Danbolt Mjøs: Norwegian physician, academic leader and Nobel Committee chair Ole Danbolt Mjøs
- Ole Ernst (Danish actor) Ole Ernst
- Ole Gunnar Solskjær
- Ole Henrik Laub
- Ole Kirk Christiansen — Danish carpenter who founded the company that became LEGO Ole Kirk Christiansen
- Ole Knapp — Norwegian Labour Party Politician and Minister of Industry Ole Knapp
- Ole Krarup — Danish law professor and European Parliamentarian Ole Krarup
- Ole Miss Rebels (University of Mississippi Athletics) Ole Miss Rebels
- Ole Petter Andreassen — Norwegian guitarist and producer Ole Petter Andreassen
- Ole Thestrup
- Ole von Beust — Mayor of Hamburg and German state politician Ole von Beust
- Ole — village on Hiiumaa, Hiiu County, Estonia Ole, Estonia
- Olea capensis — African black ironwood Olea capensis
- Oleaceae (Olive Family): Taxonomy, Characteristics, and Uses Oleaceae
- Olean, New York: A regional city on the Allegheny River Olean, New York
- Oleander (Nerium oleander) — ornamental, toxic Mediterranean shrub Oleander
- Oleg Blokhin: Ukrainian footballer, Ballon d'Or winner and manager Oleg Blokhin
- Oleg Bryzhak — Kazakh-born German bass-baritone (1960–2015) Oleg Bryjak
- Oleg Ivanovich Kovalyov — Russian regional and federal politician Oleg Ivanovich Kovalyov
- Oleg Karavaychuk — Soviet and Russian composer and pianist Oleg Karavaychuk
- Oleg Kononenko — Russian Cosmonaut Oleg Kononenko
- Oleg Pashinin
- Oleg Pavlov: Russian novelist and chronicler of late Soviet life Oleg Pavlov
- Oleg Protopopov — Soviet-Swiss pair skater and Olympic champion Oleg Protopopov
- Oleg Romantsev — Russian football manager and former player Oleg Romantsev
- Oleg Salenko
- Oleg Tabakov — Soviet and Russian actor, theatre director, and educator Oleg Tabakov
- Oleg Tverdovsky — Ukrainian-Russian Ice Hockey Defenseman Oleg Tverdovsky
- Oleg Vidov
- Oleg Yefremov — Soviet and Russian actor and theatre director Oleg Yefremov
- Oleh Babayev — Ukrainian mayor, businessman and sports patron Oleh Babayev
- Oleh Lysheha — Ukrainian poet, playwright and translator Oleh Lysheha
- Olei Hagardom: Jewish Underground Members Executed During the British Mandate Olei Hagardom
- Oleksandr O. Shevchenko — Ukrainian scientist, judge and politician (1937–2016) Oleksandr Shevchenko
- Oleksandr Shovkovskiy — Ukrainian goalkeeper and long-serving Dynamo Kyiv player Oleksandr Shovkovskiy
- Oleksandr Turchynov
- Oleksiy Honcharuk — Ukrainian politician and former prime minister Oleksiy Honcharuk
- Olen (Antwerp, Belgium) Olen
- Olendon: a commune in Calvados, Normandy Olendon
- Oles Buzina: Ukrainian journalist, writer and controversial political figure Oles Buzina
- Oleta Adams: American Singer, Pianist, and Soulful Songwriter Oleta Adams
- Oleum (fuming sulfuric acid) Oleum
- Oleyres — former municipality in Vaud, Switzerland Oleyres
- Olfaction (Sense of Smell): Biology, Function, and Significance Olfaction
- Olfactory bulb — structure, function and significance Olfactory bulb
- Olfactory system: structure, function, and role in vertebrate behavior Olfactory system
- Olga Bondarenko
- Olga Feliú — Chilean lawyer and senator (1932–2017) Olga Feliú
- Olga Harmony — Mexican Playwright and Drama Educator Olga Harmony
- Olga Knyazeva — Soviet Olympic Foil Fencer Olga Knyazeva
- Olga Korbut — gymnast whose acrobatics reshaped Olympic women's gymnastics Olga Korbut
- Olga Krzyżanowska
- Olga Kurylenko: French actress and model Olga Kurylenko
- Olga Sawicka — Polish prima ballerina and choreographer Olga Sawicka
- Olga Syahputra
- Olga Tañón — Puerto Rican merengue and Latin pop singer Olga Tañón
- Olga Tass (Lemhényi) — Hungarian Olympic Gymnast (1929–2020) Olga Tass
- Olga Tokarczuk: Polish novelist, essayist and Nobel laureate Olga Tokarczuk
- Olia Chain (The Olias) — mountain range in southwest Northern Territory Olia chain
- Oliena, Sardinia — town, landscape, wine and cultural heritage Oliena
- Oligarchy: rule by a few — definition, history, types and modern contexts Oligarchy
- Oligocene epoch Oligocene
- Oligochaete — segmented worms of the class Clitellata Oligochaete
- Oligopoly: market structure dominated by a few interdependent firms Oligopoly
- Oligopsony: market power when few buyers dominate Oligopsony
- Oligosaccharide: structure, types, biological roles and uses Oligosaccharide
- Oligotroph: organisms adapted to nutrient-poor environments Oligotroph
- Olin J. Eggen
- Olin, Iowa — small city profile and community overview Olin, Iowa
- Olinguito (Bassaricyon neblina): a cloud‑forest mammal of the Andes Olinguito
- Olive (Olea europaea): fruit, tree, oil, and cultural importance Olive
- Olive (color) a color which looks like green or yellow
- Olive (fruit): biology, processing, uses, and cultural significance Olive (fruit)
- Olive and the Rhyme Rescue Crew
- Olive Garden: American Italian-American Casual Dining Chain Olive Garden
- Olive Hill, Kentucky: small city in northeastern Kentucky Olive Hill, Kentucky
- Olive oil: production, types, uses, and health aspects Olive oil
- Olive ridley sea turtle (Lepidochelys olivacea) Olive ridley sea turtle
- Olive Thomas: Silent‑era actress, model, and an early Hollywood scandal Olive Thomas
- Olive tree (Olea europaea) Olive tree
- Olivenza: the Iberian territorial dispute between Portugal and Spain Olivenza
- Oliver & Company — Disney's 1988 New York–Set Animated Musical Oliver & Company
- Oliver Batali Albino
- Oliver Bierhoff
- Oliver County, North Dakota
- Oliver Cromwell: soldier, statesman, and the Protectorate era Oliver Cromwell
- Oliver Dragojević — Croatian singer-songwriter and cultural icon Oliver Dragojević
- Oliver E. Williamson
- Oliver Ellsworth: Founding-Era Lawyer, Senator and Chief Justice Oliver Ellsworth
- Oliver Glasner — Austrian football coach and former player Oliver Glasner
- Oliver Goldsmith: Life, Major Works, and Literary Legacy Oliver Goldsmith
- Oliver Goonetilleke — First Ceylonese Governor‑General (1892–1978) Oliver Goonetilleke
- Oliver Hardy