| Opiinae | Opiliaceae | Opilioacarida |
| Opilioacaridae | Opilioacariformes | Opilioacaroidea |
| Opiliones | Opilo | Opilo domesticus |
| Opinel | Opinio juris | Opiothorax |
| Opisthobranchia | Opisthocentrus | Opisthocentrus ocellatus |
| Opisthocoelia | Opisthocomi | Opisthocomidae |
| Opisthocomiformes | Opisthocomus | Opisthocomus crisiatus |
| Opisthocomus hoazin | Opisthokonta | Opisthonema |
| Opisthonema oglinum | Opisthoproctidae | Opisthoproctus |
| Opisthoproctus soleatus | Opisthopsis | Opisthorchis |
| Opisthorchis felineus | Opisthoscyphus | Opisthothelae |
| Opithandra | Opithandra primuloides | Opium |
| Opium (альбом KMFDM) | Opius | Opiz |
| OPJM | OPL | OPL (киберспорт) |
| OPL Split 1 2015 | OPL Split 2 2015 | OPL Spring 2016 |
| OPL2 | OPL3 | Oplismenus abortivus |
| Oplismenus intermedius | OPLL | Oplopanax |
| Oplopanax elatus | Oplosia | Oplosia cinerea |
| Oplukion | Opluridae | Oplurinae |
| OPM Россия | OPM3 | OPML |
| OPN | OPN2 | OPNsense |
| Opodiphthera | Opophytum | Opostega |
| Opostegidae | Opostegoides | Oppa Is Just My Style |
| Oppa is just my style | Oppenheim Meret | Opple Lighting |
| Oppna din dorr | Oppo | OPPO |
| OPPO Electronics | Opportunities (Let's Make Lots Of Money) | Opportunities (Let’s Make Lots of Money) |
| Opportunities (Let’s Make Lots Of Money) | Opportunity | Opportunity rover |
| Opposed piston engine | Opposing Force | OPQ |
| Oprah Gail Winfrey | Oprah Winfrey | Oprah Winfrey Network |
| OPS-24 | Opsantha | Opsanus tau |
| Opsilia | Opsilia coerulescens | Opsimea |
| Opsimea nigripennis | OpsMgr | OPT |
| Opt-out (Европейский союз) | Optane | Optare |
| Optatam Totius | Opteron | Optical Character Recognition |
| Optical character recognition | Optical Gravitational Lensing Experiment | Optics |
| Optilete | OPTIMA-WorkFlow | Optimal asymmetric encryption padding |
| Optimal Asymmetric Encryption Padding | OptimFROG | Optimization (конференция) |
| Optimus | Optimus maximus | Optimus Prime |
| Optimystica Orchestra | Option (клавиша) | Optioservus |
| OptiPNG | OptiX | Opulaster intermedius |
| Opulaster opulifolius | Opuntia | Opuntia bigelovii |
| Opuntia ficus-indica | Opuntia megacantha | Opuntia microdasys |
| Opuntiaceae | Opuntioideae | Opuntiopsis |
| Opus | Opus (группа, Австрия) | Opus (звукозаписывающий лейбл) |
| Opus (кодек) | Opus (лейбл) | Opus Dei |
| Opus Dei (альбом) | Opus Dementiae - Per Speculum Et In Aenigmate | Opus Dementiae – Per Speculum et in Aenigmate |
| Opus Dementiae — Per Speculum Et In Aenigmate | Opus Discovery | Opus Eponymous |
| Opus Imperfectum | Opus magnum | Opus Magnum |
| Opus Prize | Opus quadratum | Opus reticulatum |
| Opus sectile | Opus testaceum | Opus utique oppr. |
| OQJAV | OR | ORA |
| Ora Carew | Ora et labora | Oraa Guzura Dado |
| Oracle | Oracle (СУБД) | Oracle (значения) |
| ORACLE (компьютер) | Oracle ADF | Oracle ApEx |
| Oracle Apex | Oracle APEX | Oracle Application Express |
| Oracle Applications | Oracle arena | Oracle Arena |
| Oracle Cluster File System | Oracle Corporation | Oracle Database |
| Oracle Database Machine | Oracle E-Business Suite | Oracle eBusiness Suite |
| Oracle Enterprise Linux | Oracle Enterprise Service Bus | Oracle Forms |
| Oracle Fusion Middleware | Oracle Grid Engine | Oracle Java |
| Oracle JDeveloper | Oracle Linux | Oracle of the City of San Francisco |
| Oracle Open Office | Oracle OpenWorld | Oracle PowerBrowser |
| Oracle Primavera | Oracle RAC | Oracle Rdb |
| Oracle RDBMS | Oracle Reports | Oracle Siebel CRM |
| Oracle Solaris | Oracle Solaris Studio | Oracle Spatial and Graph |
| Oracle SQL Developer | Oracle Unbreakable Linux | Oracle Unified Method |
| Oracle Weblogic Server | Oracle WebLogic Server | Oracle9i |
| Oracular Spectacular | Orage | Oral Fixation 2 |
| Oral Fixation Tour | Oral Fixation Vol. 2 | Oral Fixation Vol. 2 (альбом) |
| Oral Fixation, Vol. 2 | Oral Fixation, Vol. 2 (альбом) | Oral history |
| Oral-B | Oramel Hinckley Simpson | Orange |
| Orange (значения) | Orange (манга) | Orange Armenia |
| Orange Bowl | Orange Box | Orange Business Services |
| Orange Caramel | ORANGE CARAMEL | Orange County Choppers |
| Orange County, Florida | Orange County, Indiana | Orange County, New York |
| Orange County, North Carolina | Orange County, Texas | Orange County, Vermont |
| Orange County, Virginia | Orange GGN | Orange Goblin |
| Orange Israel | Orange Juice | Orange Moldova |
| Orange Prokom Open | Orange Prokom Open 2007 | Orange Range |
| ORANGE RANGE | Orange Romeda | Orange SA |
| Orange Tiga | Orange Warsaw Open | Orangeburg |
| Orangeburg County, South Carolina | OrangeCD Player | Orangina |
| Orania | Orano | Orapia |
| Oratio principis | Oratosquilla oratoria | Oravec |
| Orazio Fiume | Orazio Vecchi | Orígenes |
| Orb | Orb (браузер) | Orbcomm-G2 |
| Orbea | Orbest | Orbigny |
| Orbiliaceae | Orbiliales | Orbiliomycetes |
| Orbiniidae | Orbis terrae | Orbis terrarum |
| Orbit | Orbit (жевательная резинка) | Orbit Books |
| Orbit Downloader | Orbit@home | Orbital |
| Orbital (альбом) | Orbital (значения) | Orbital ATK |
| Orbital Sciences | Orbital Sciences Corporation | Orbital Skyhook |
| Orbiter | Orbiter (значения) | Orbiter (БПЛА) |
| Orbitum | Orbix | Orc |
| Orc (Warcraft) | Orca | ORCA |
| Orca (альбом) | Orca Airways | Orca Browser |
| Orca orca | OrCAD | Orcaella |
| Orcaella brevirostris | Orcaella heinsohni | Orchesella erpeldingae |
| Orchesella hoffmanni | Orchestra Baobab | Orchestral Manoeuvres in the Dark |
