| Prefix | Organization | Purpose | Web Site | Contact | Registered |
|---|---|---|---|---|---|
| O | Orcka Development | Various | www.orcka.com | Simon Carter | 05-Aug-2001 |
| OA | Alassiry Information Technology | www.alassiry.com/ | Osama ALASSIRY | 16-Jun-1999 | |
| oad | SteelToad Software, Inc. | All | www.steeltoad.com | Ray Andrews | 06-Jan-2000 |
| OC | Orelle Corporation | Reserved; Reserved | Philip Cain | 06-Jun-1998 | |
| OCI | Nica-Com ltd. | NCOCI8 library | www.ncom.ru/diman/index.html | Dmitry Arefiev | 01-Mar-2000 |
| OCL | OfficeCraft Limited | Reserved | www.officecraft.co.uk | Dave Craggs | 07-Apr-1999 |
| OD | Olivier Dahan | Reserved; Reserved | Olivier Dahan | 24-May-1998 | |
| OD | Orchid Data | Various | James Baile | 12-May-1999 | |
| OD | My Power Station Technology PTY Ltd | Component Name Prefix | www.mypowerstation.biz | David Lipschitz | 22-Jan-2013 |
| ODAC | CoRe Lab | Oracle Data Access Components | www.crlab.com | Dmitry Nik | 18-Oct-1999 |
| ODI | Odilon Nelson | Reserved; Reserved | www.odilon.home.ml.org | Odilon Nelson | 01-Feb-1999 |
| odm | Vertis Direct Marketing Services Ltd | www.vertis.co.uk | Chris Parkinson | 04-Aug-2004 | |
| ODS | Dovetail Data Systems Ltd. | Reserved; Reserved | Oliver Stogdon | 19-Mar-1999 | |
| OFD | KKK | tdbcaledit;thusogrid | faruk demirel | 10-Oct-1999 | |
| OFW | Oosterkamp training | consultancy | Oosterkamp Framework | www.oosterkamp.nl | Taco J. Oosterkamp | 18-Nov-1999 |
| OG | TurboPower Software Company | OnGuard; Security | www.turbopower.com | Julian M Bucknall | 16-May-1998 |
| OIG | Oliver Informatik GmbH | www.spoc42.com | Stephen Oliver | 23-Apr-1999 | |
| OJ | janko.at | Otto Janko | 11-Feb-2000 | ||
| OM | Object Mastery P/L | Reserved; Reserved | www.objectmastery.com | John Vander Reest | 06-Jun-1998 |
| ome | Omega Point | www.omega-point.com | Rik Watson | 21-Mar-2000 | |
| OMS | TrueSoft Corporation | Order Management System | truesoftnet.com | Tom Rue | 01-Jun-1999 |
| ON | PineFive EIS | General Utils and GUI | www.pinefive.com | ofer narkis | 25-Aug-2001 |
| OO | Obvious Objects | ooCoolMemo; Memo | www.avatarsoft.com/obvious | Chad Jones | 13-Sep-1998 |
| OO | OO Designs Ltd | www.OODesigns.Com | Michael Lindre | 26-Apr-1999 | |
| OOD | OO Designs Ltd | Reserved | www.OODesigns.Com | Michael Lindre | 09-Apr-1999 |
| OP | Visual Interface Programming Services | Reserved; Reserved | www.bigfoot.com/~objectpascal | Curt T. Smith | 04-Aug-1998 |
| OPL | GERALDO LOPES DE SOUZA | Open Persistence Layer | GERALDO LOPES DE SOUZA | 08-Feb-2002 | |
| OPL | GERALDO LOPES DE SOUZA | Open Persistence Layer | GERALDO LOPES DE SOUZA | 08-Feb-2002 | |
| OPT | Max. I.T. Pty. Ltd. | Optimum Suite | Tim Blizard | 28-Sep-1999 | |
| OPTO | Professional Practice Systems, Inc. | Reserved | Scott Bussinger | 07-Apr-1999 | |
| Oq | OQ Services | All Oq components | www.oq-services.com | Marjan Venema | 20-Nov-1999 |
| Oq | OQ Services | All OQ components | www.oqservices.com | Marjan Venema | 14-Jun-2000 |
| OR | Oriana-Automatisering | Reserved | www.Oriana-Automatisering.com | Geurt Lagemaat | 21-Oct-1999 |
| ORB | My Power Station Technology (Pty) Ltd. | www.mypowerstation.biz | David Lipschitz | 04-Aug-1998 | |
| ORD | Ordiges | Reserved; Reserved | www.ordiges.be | Paul Coomans | 19-Mar-2099 |
| OS | OSInet | FFC; Database | www.osinet.fr | Frederic G. MARAND | 01-Feb-1999 |
| OSS | Optical Services - Scandinavia | www.optical.dk | Kim Madsen | 21-Apr-1999 | |
| OST | Objective Software Technology | In Development; Reserved | www.obsof.com | James Heyworth | 03-May-1998 |
| OV | Object Vision Associates | reserved | www.objvision.com | Rick McGee | 16-Sep-1999 |
| OV | Onno Veersma | Onno Veersma | 03-Dec-1999 | ||
| ova | Object Vision Associates | Object Tools | www.objvision.com | Rick McGee | 08-Feb-2000 |
| OVC | TurboPower Software Company | Orpheus; DataControls | www.turbopower.com/ | Julian M Bucknall | 18-May-1998 |
| OX | Opaque Software | OxPersist; Toolkit | www.opaquesoftware.com/ | Brett Liddicoet | 02-May-1998 |
| OX. | Opaque Software | Venus; Toolkit | www.opaquesoftware.com/ | Brett Liddicoet | 27-Apr-1998 |
| OZ | OzSoft | Reserved; Reserved | incolor.inetnebr.com/osborn/ | Cory Osborn | 12-May-1998 |
| Oz | OzmoSys | Reserved | Steve Forbes | 21-Nov-1999 | |
| Oz | OzmoSys | Steve Forbes | 17-Jan-2000 | ||
| Oz | OzmoSys | All | Steve Forbes | 05-Aug-2001 | |
| Ozm | OZM Research s.r.o. | Reserved | www.ozm.cz | Ivo Bauer | 22-Jan-2013 |