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- Oblivia: An archipelago in Pokémon Ranger: Guardian Signs.
- Oceania: totalitarian superstate centered on the Americas in George Orwell's Nineteen Eighty-Four.
- Ohtar: Middle Eastern country in the 1984 Goldie Hawn film Protocol
- Okenland: Oliver's imaginary country in an episode of Hannah Montana.
- Olifa: Southern American country in the John Buchan novel The Courts of the Morning.
- Olympic City: from Need for Speed: Underground.
- Onabushka: a country featured in one episode of The Navy Lark.
- Opar: a lost city-state whose inhabitants have become subhuman in the Tarzan series by Edgar Rice Burroughs.
- Opet: a Southern African country in the novel The Sunbird by Wilbur Smith, founded by Phoenicians fleeing from Carthage after the Punic Wars.
- Opperland: a country based on the Netherlands where the Dutch language is treated entertainingly.
- Opium: a narrow strip of land in between Mexico and the United States is the main location in Nancy Farmer's science fiction novel The House of the Scorpion
- Orange Archipelago or Orange Islands: a region in the Pokémon anime.
- Orangeland: Used in military scenarios by NATO countries, often warring against Blueland
- Orb Union (also United Emirates of Orb): a small island nation east of Indonesia in the anime Mobile Suit Gundam SEED Destiny.
- Oriense: is the name of the setting of Final Fantasy Type-0. It consists of four nations that until recently had coexisted peacefully.
- Oriosa: Tarrant Hawkin's home country in Michael A. Stackpole's The Dragon Crown War Cycle.
- Orre: a region in the video games Pokémon Colosseum & Pokémon XD: Gale of Darkness.
- Orsinia: a Central European country similar to Czechoslovakia or Hungary, the focus of Ursula Le Guin's Orsinian Tales and the novel Malafrena.
- Osaze: The new name of Egypt in Tim LaHaye's and Jerry B. Jenkins' novel, Kingdom Come
- Osterlich: nation invaded by Bacteria and Tomainia in the film The Great Dictator; obviously a stand-in for Austria (Osterreich)
- Ostnitz: a European country on the Cold War frontier in the computer game Border Zone.
- Ovitznia: a republic in the Balkans from Road Rovers TV series.
- Osea: a major superpower in the video game Ace Combat 5: The Unsung War and other games in the Ace Combat series.
- Ostrichishishouia: a fake country that PJ from good Luck Charlie made up in the episode Meet The Parents.
- Outer Heaven: a fortified military state in the video game Metal Gear.
- Oz, Land of Oz: magical land in L. Frank Baum's Oz books, as well as the later novel, movie The Wizard of Oz and play Wicked and its sequels.
Read more about this topic: List Of Fictional Countries