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Novyy Island
Novyy Island is the United States name for Novyj, Kupol, a small Antarctic island at 70°50'S, 2°50'W listed in the Russia Gazetteer and SCAR Composite Gazetteer; the name Ostrov Novyy also denotes islands in Siberia and Kazakhstan.
Nunivak Island
Nunivak Island: volcanic Bering Sea island off western Alaska, third largest off the Alaskan coast, home to Mekoryuk village and the muskox herd reintroduced from Greenland in the 1930s, source of Alaska's muskox translocations.
Nusa Penida
Nusa Penida: largest of Bali's three Nusa islands in Klungkung Regency, Indonesia; a 2010 marine protected area with 296 coral and 576 fish species, IMO PSSA since 2024, and a major tourism destination facing carrying-capacity limits.
Oahu
Oahu (Oʻahu), Hawaii's third largest island and "The Gathering Place," formed by the Waianae and Koolau shield volcanoes; holds Honolulu, about 69% of the state's population, Pearl Harbor, and six traditional moku districts.
Oak Island
Oak Island (Nova Scotia) is a privately owned Mahone Bay island tied to the Money Pit treasure legend dating to 1795; no treasure has been proven, early accounts lack contemporary evidence, and the story is now popularized by The Curse of Oak Island.
October Revolution Island
October Revolution Island (Ostrov Oktyabrskoy Revolyutsii), largest island of Severnaya Zemlya, Krasnoyarsk Krai, Russia; 14,200 km², 965 m Mount Karpinsky, over half glaciated, charted 1930–32 by Ushakov and Urvantsev.
Ohlin Island
Ohlin Island, also called Bailys Island, is a 170 m high uninhabited island in the Palmer Archipelago, Antarctica, about 11 km west of Tower Island, discovered by the Swedish Antarctic Expedition 1901–04 and named by Nordenskjöld for zoologist Axel Ohlin.
Okinawa Island (沖縄)
Okinawa Island (沖縄島, Okinawa-jima), also Okinawa Main Island, is the largest Ryukyu island, Japan: about 1,207 km², 1.35 million people, Naha capital, Ryukyu Kingdom heritage, 1945 battle, US bases.
Okinotorishima (沖ノ鳥島)
Okinotorishima (沖ノ鳥島), also called Parece Vela, is a coral reef about 1,700 km south of Tokyo that is Japan's southernmost island, with only two small islets above sea level.
Ōkunoshima (大久野島)
Ōkunoshima (大久野島), "Rabbit Island," is a small Hiroshima Prefecture island in the Seto Inland Sea, formerly a secret Imperial Japanese Army poison gas plant (1929–1945, ~6,500 tons) and now a tourist site with introduced feral European rabbits.
Öland
Öland (Ölandsbron link) is a 140-km-long Swedish limestone island in the Baltic Sea, home to Stora Alvaret, Europe's largest alvar, and the UNESCO Agricultural Landscape of Southern Öland inscribed in 2000.
Old Harry Rocks
Old Harry Rocks: chalk stacks, arches, and stumps at Handfast Point, Ballard Down, Dorset, eastern end of the Jurassic Coast World Heritage Site; Upper Cretaceous chalk once continuous with the Isle of Wight's Needles.
Olympic Peninsula
The Olympic Peninsula is a roughly triangular peninsula in northwestern Washington, bordered by the Pacific Ocean and the Strait of Juan de Fuca, home to Mount Olympus (7,980 ft), temperate rain forests, Olympic National Park, and eight tribes.
Ometepe
Ometepe (Isla de Ometepe), Nicaragua's 276 km² volcanic island in Lake Cocibolca, formed by active Concepción (1,610 m) and dormant Maderas (1,394 m), a UNESCO biosphere reserve since 2010.
Orcas Island
Orcas Island, the largest of Washington's San Juan Islands at about 57 square miles, lies in the Salish Sea; its Mount Constitution rises 2,409 feet, and Eastsound is its main village.
Orkney
Orkney, a Scottish archipelago of 68+ islands (990 km², 16 inhabited) north of mainland Scotland, with capital Kirkwall, Norse heritage, the Heart of Neolithic Orkney World Heritage Site, and the EMEC marine energy test centre.
Orust
Orust is an island and municipality in Bohuslän, Västra Götaland, Sweden; the largest island on the west coast (386 km²), seat Henån, 15,363 inhabitants in 2025, known for boatbuilding and fishing villages.
Osa Peninsula
Osa Peninsula, southwestern Costa Rica Pacific peninsula (~1,500 km2) harboring 2.5% of global terrestrial biodiversity, Corcovado National Park, the Osa Mélange, and Cocos Ridge subduction uplift.
Ostrov Bel’kovskiy
Ostrov Bel'kovskiy (Belkovsky Island, Остров Бельковский) is the westernmost of the Anzhu Islands in the New Siberian Islands, Russia, west of Kotelny across the Strait of Zarya; uninhabited tundra up to 127 m with walrus haulouts and Permian-Triassic trap magmatism.
Ostrov Bol’shevik
Ostrov Bol'shevik (остров Большевик), Bolshevik Island, is the southernmost, second-largest island of Severnaya Zemlya, Russia: about 11,300 km², 935 m high, ~30% glaciated, separated from Taymyr by Vilkitsky Strait, with accelerating glacier retreat and Cape Baranov research station.
Ostrov Bol’shoy Shantar
Bolshoy Shantar (Большой Шантар) is the largest island of the Shantar archipelago in the western Sea of Okhotsk, Khabarovsk Krai, Russia; about 1,790 km², with brackish Lake Bolshoe, Yakshina Bay meteorological station, and inclusion in Shantar Islands National Park since 2013.
Ostrov Gallya
Ostrov Gallya (Остров Галля, Hall Island) is the fifth largest island of Franz Josef Land, Russia, about 1049-1200 km², 93.8% glacier-covered, highest point 502 m, discovered 1874 by the Austro-Hungarian Tegetthoff expedition.
Ostrov Gukera
Ostrov Gukera (остров Гукера, Hooker Island) is an island in the Franz Josef Land archipelago, best known for Bukhta Tikhaya, the first Soviet polar station on the archipelago, opened in 1929.
Ostrov Kamenka
Ostrov Kamenka (Остров Каменка), also rendered Ostrov Kamenka-Sar, is an inhabited island in western Lake Pskov in Pechorsky District, Pskov Oblast, northwestern Russia, part of a protected natural monument designated in 2007.
Ostrov Matar
Ostrov Matar (остров Матар) is a small uninhabited island in the Anzhu Islands of the New Siberian archipelago, East Siberian Sea, Yakutia, Russia; about 8 km², 5 km long, near Bunge Land and Zheleznyakov Island.
Ostrov Mezhdusharskiy
Ostrov Mezhdusharskiy (Остров Междушарский), also Mezhdusharski, is the third largest island of Russia's Novaya Zemlya archipelago, 742 km², in the Barents Sea west of Yuzhny Island, separated by Kostin Shar strait.
Ostrov Pioner
Ostrov Pioner (Остров Пионер, Pioneer Island) is an uninhabited 1,527 km² island in northwestern Severnaya Zemlya, Kara Sea, Krasnoyarsk Krai, Russia; highest point 385 m, discovered by Ushakov and Urvantsev in 1930–32.
Ostrov Severnyy
Ostrov Severnyy (Остров Северный), or Severny Island, is the northern of the two large islands of Novaya Zemlya in the Russian Arctic, belonging to Arkhangelsk Oblast.
Ostrov Sibiryakova
Ostrov Sibiryakova (Остров Сибирякова), or Kuz'kin Island, is an ~800 km² flat tundra island in the southern Kara Sea at the entrance to the Yenisei Gulf, Krasnoyarsk Krai, named by Nordenskiöld in 1878 and part of the Great Arctic Reserve.
Ostrov Solsberi
Ostrov Solsberi (Остров Солсбери), also called Salisbury Island, is a largely glaciated island in central Franz Josef Land, Russia, the largest of the Zichy Land group.