O
- Octavia (Roman personality: Claudia Octavia)
- GWR Standard Goods 0-6-0 (1855 - 1873)
- Olympus (Greek mythology: Mount Olympus)
- GWR Standard Goods 0-6-0 (1861 - 1879)
- Orion (Greek personality: Orion of Thebes)
- GWR Fire Fly class 2-2-2 (1842 - 1867)
- SDR Comet class 4-4-0ST (1853 - 1878)
- Orpheus (Greek mythology: Orpheus)
- GWR Standard Goods 0-6-0 (1861 - 1877)
- Oscar (Famous personality: Oscar I of Sweden)
- GWR Victoria class 2-4-0 (1856 - 1880)
- Orson
- GWR Standard Goods 0-6-0 (1854 - 1874)
- Osiris (Egyptian mythology: Osiris)
- SDR Comet class 4-4-0ST (1853 - 1873)
- GWR Standard Goods 0-6-0 (1855 - 1877)
- SDR Leopard class 4-4-0ST (1875 - 1892)
- Ostrich (Bird: Ostrich)
- GWR Fire Fly class 2-2-2 (1840 - 1865)
- SDR Comet class 4-4-0ST (1852 - 1877)
- GWR Hawthorn class 2-4-0 (1865 - 1877)
- GWR Hawthorn class 2-4-0T (1877 - 1892)
- Otho (Famous personality: Otto of Greece)
- GWR Victoria class 2-4-0 (1856 - 1880)
- Ovid (Roman personality: Ovid)
- GWR Bogie class 4-4-0ST (1854 - 1873)
- Owl (Bird: Owl)
- SDR Owl class 0-4-0WT (1873 - 1893)
- Oxford (Geography: Oxford)
- GWR Swindon class 0-6-0 (1866 - 1874)
Read more about this topic: List Of Broad Gauge (7 Feet) Railway Locomotive Names