| Ophrys lutea | Ophrys mammosa | Ophrys monophyllos |
| Ophrys oestrifera | Ophrys scolopax | Ophrys speculum |
| Ophrys sphegodes subsp. mammosa | Ophrys spiralis | Ophrys taurica |
| Ophrys tenthredinifera | Ophrysia | Ophrysia superciliosa |
| Ophthalmopone | Ophthalmosauridae | Ophthalmosaurus |
| OPIC | OPIE | Opie |
| Opiellus | 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) |
