| Oostkamp | Oostrozebeke | Ooststellingwerf |
| Oostzaan | Ootheca (chi bọ cánh cứng) | Ootheca apicalis |
| Ootheca apicicornis | Ootheca bennigseni | Ootheca bicolor |
| Ootheca bifrons | Ootheca bourguii | Ootheca chapuisi |
| Ootheca costulata | Ootheca donckieri | Ootheca flavicollis |
| Ootheca frontalis | Ootheca fulvipes | Ootheca kibonotensis |
| Ootheca laevipennis | Ootheca longula | Ootheca minuta |
| Ootheca modesta | Ootheca mutabilis | Ootheca nigrilabris |
| Ootheca orientalis | Ootheca podagrica | Ootheca proteus |
| Ootheca punctata | Ootheca semicaeurlea | Ootheca unicolor |
| Ootheca variabilis | Ootheca variceps | Ootheca vittata |
| Ootypus globosus | OOXML | Oozora Tsubasa |
| Opařany | Opacibidion opacicolle | Opacibidion rugicolle |
| Opacibidion sulcicorne | Opacinota | Opacinota bisignata |
| Opacographa | Opacoinvolvulus adjectus | Opacoinvolvulus aterrimus |
| Opacoinvolvulus birmanicus | Opacoinvolvulus civicus | Opacoinvolvulus cognatus |
| Opacoinvolvulus contristatus | Opacoinvolvulus furvus | Opacoinvolvulus gensanensis |
| Opacoinvolvulus intricatus | Opacoinvolvulus intrusus | Opacoinvolvulus lepidus |
| Opacoinvolvulus lygaeus | Opacoinvolvulus nigricans | Opacoinvolvulus nitidifrons |
| Opacoinvolvulus penangicolus | Opacoinvolvulus planiusculus | Opacoinvolvulus pseudocivinus |
| Opacoinvolvulus punctifrons | Opacoinvolvulus punctulatus | Opacoinvolvulus rottensis |
| Opacoinvolvulus ruficornis | Opacoinvolvulus rugiceps | Opacoinvolvulus scitus |
| Opacoinvolvulus semirugosus | Opacoinvolvulus subopacus | Opacoinvolvulus zherichini |
| Opades costipennis | Opadometa | Opadometa fastigata |
| Opadometa grata | Opaka | Opaka (đô thị) |
| Opal | Opal goodeid | Opalenica |
| Opalia (động vật chân bụng) | Opalia (chi ốc biển) | Opalia (Epitoniidae) |
| Opallionectes | Opamyrma | Opamyrma hungvuong |
| Opan | Opan (đô thị) | Opanassenkovius verrucosus |
| Opanözü, Tavşanlı | Oparanthus | Oparanthus albus |
| Oparanthus coriaceus | Oparanthus hivoanus | Oparanthus rapensis |
| Oparanthus teikiteetinii | Oparara | Oparara karamea |
| Oparara vallus | Oparinsky (huyện) | Opas |
| Opas caudacuta | Opas caudata | Opas lugens |
| Opas melanoleuca | Opas paranensis | Opas trilineata |
| Opatów | Opatija | Opatov, Jihlava |
| Opatov, Svitavy | Opatov, Třebíč | Opatovec |
| Opatovice I | Opatovice nad Labem | Opatovice, Brno-venkov |
| Opatovice, Přerov | Opatowski | Opatrini |
| Opatrinus pullus | Opava | Opava (huyện) |
| Opéra | Opéra (định hướng) | Opéra Bastille |
| Opéra Comique | Opéra comique | Opéra de Paris |
| Opéra Garnier | Opéra national de Paris | Opéra-Comique |
| Opdyke West, Texas | Opeatocerus purpurata | Opeatostoma |
| Opeatostoma pseudodon | OPEC | Opel |
| Opelika, Alabama | Opelousas, Louisiana | Open 13 |
| Open Arms (bài hát của Journey) | Open Automotive Alliance | Open Championship |
| Open Database Connectivity | Open ERP | Open Geospatial Consortium |
| Open Graphics Project | Open Office | Open proxy |
| Open Road Films | Open Season (phim 2006) | Open Season 2 |
| Open Season 3 | Open Society Foundations | Open Source |
| Open Street Map | Open Street Map Foundation | Open World Entertainment |
| Open XML | Open Your Heart | Open Your Heart (bài hát của Madonna) |
| Open Your Heart (bài hát) | OpenCity | OpenCola |
| OpenCourseWare | OpenDNS | OpenDocument |
| OpenERP | OpenEXR | OpenGL |
| OpenHPI | OpenID | OpenLeaks |
| OpenMosix | OpenOffice | OpenOffice Basic |
| OpenOffice.org | Openoffice.org | OpenOffice.org Base |
| OpenOffice.org Calc | OpenOffice.org Draw | OpenOffice.org Impress |
| OpenOffice.org Math | OpenOffice.org Writer | OpenShift |
| OpenSkies | OpenSocial | OpenSSH |
| OpenSSL | Openssl | OpenSsl |
| OpenStack | OpenStreetMap | Openstreetmap |
| OpenStreetMap Foundation | OpenSUSE | OpenType |
| OpenVPN | OpenWire (giao thức nhị phân) | OpenWrt |
| Opera | Opera (định hướng) | Opera (trình duyệt web) |
| Opera (trình duyệt) | Opera de Paris | Opera Fidelio |
| Opera House Sydney | Opera Mini | Opera mini |
| Opera National de Paris | Opera national de Paris | Opera seria |
| Opera Software | Opera Sydney | Opera xà phòng |
| Opera, Milano | Operação Prato | Operatic pop |
| Operating system | Operation Deliberate Force | Operation Ivy |
| Operation Mincemeat | Operation Sandstone | Operation Smile |
| Operation Smile Việt Nam | OperaTor | Operatsiya Silent Storm |
| Operavox | Operavox : Hành trình khó quên với nhạc kịch và hoạt họa | Opercularia |
| Opercularia acolytantha | Opercularia apiciflora | Opercularia aspera |
| Opercularia diphylla | Opercularia echinocephala | Opercularia hirsuta |
| Opercularia hispida | Opercularia hispidula | Opercularia loganioides |
| Opercularia ovata | Opercularia rubioides | Opercularia scabrida |
| Opercularia spermacocea | Opercularia turpis | Opercularia vaginata |
| Opercularia varia | Opercularia volubilis | Operculicarya gummifera |
| Operculina ampliata | Operculina aurea | Operculina codonantha |
| Operculina grandiflora | Operculina hamiltonii | Operculina macrocarpa |
| Operculina palmeri | Operculina pinnatifida | Operculina pteripes |
| Operculina rhodocalyx | Operculina sericantha | Operculina triquetra |
| Operculina turpethum | Operculiphorus tubifer | Operetta |
| Operon | Operon lac | Operophtera |
| Operophtera boreata | Operophtera bruceata | Operophtera brumata |
| Operophtera brunata | Operophtera brunnea | Operophtera brunnescens |
| Operophtera crispifascia | Operophtera fagata | Operophtera fasciata |
| Operophtera fusca | Operophtera grisearia | Operophtera groenlandica |
| Operophtera harrisoni | Operophtera huenei | Operophtera hyemata |
| Operophtera hyperborea | Operophtera isaaki | Operophtera japonaria |
| Operophtera latipennis | Operophtera marginata | Operophtera myricaria |
| Operophtera myrtillivora | Operophtera nana | Operophtera nexifasciata |
| Operophtera nigrescens | Operophtera occidentalis | Operophtera peninsularis |
| Operophtera phryganea | Operophtera pygmaeata | Operophtera rectipostmediana |
| Operophtera relegata | Operophtera remotata | Operophtera tenerata |
| Operophtera unicolor | Operophtera vulgaris | Opesia atrata |
