| Obscuro Labs | |
| OceanoBe Technology | |
| Oceanus Software | Bucharest |
| Octagram Creative S.R.L. | |
| Octavic PTS S.R.L. | |
| Octogram | |
| Odas Global Consulting | Cluj |
| Odysee Softserv | Bucharest |
| OferteIT | Sibiu |
| Office Max S.R.L. | Bucharest |
| officerentinfo.ro | |
| Ogre | |
| OkkWebMedia S.R.L. | Cluj |
| Omega Consulting | |
| Omniconvert | Bucharest |
| OMS Software | |
| Omubo Design | |
| One Designs | Bucharest |
| One Solution Media & Advertising S.R.L. | |
| Onefox | |
| OneShopping.ro | Vâlcea |
| Onix S.r.l. | Vâlcea |
| Online Booking Manager S.R.L. | Dolj |
| Online Hub | |
| OnTarget | |
| Ontegra Solutions | |
| Open Public Services | |
| OPEN Web Design S.R.L. | Brăila |
| Opera CRO | |
| OPTI Software | |
| Opticnet | Bucharest |
| Optima Group | Bucharest |
| OptimizareSEOro | |
| Oracle Romania | Bucharest |
| Orange Fab România | Bucharest |
| Orange România | |
| Oranta IT Solutions | Cluj |
| Ordmark S.R.L. | Bucharest |
| ORESA Ventures | Bucharest |
| Outside Software, Inc. | Bucharest |
| Oveus S.R.L. | Bucharest |
| Oxygen IT | Bucharest |
| Oxygen XML Editor | Dolj |
| OZ Web Design | Brașov |
| P4B | |
| P92 Digital | |
| PadiCode S.R.L. | |
| Pagelocity | Dolj |
| Pago | Bucharest |
| Pandora | Bucharest |