| ob3 | ORTIMzeit Data File |
| obc | AICON 3D Photogrammetry File |
| obg | ZBrush Mesh Data |
| obi | Microsoft Outlook RSS Subscription Data |
| obj | Wavefront Object File |
| objf | STRIPE Object Data |
| obk | Genie Outlook Express Backup Data |
| obk | Oxygen Phone Manager Phone Book Data |
| obpack | ObjectBar Theme |
| obs | AquaCrop Field Observations Data |
| obs | Open Broadcaster Software Data |
| obs | WAsP Obstacle List |
| obs-service | Open Broadcaster Software Data |
| obskin | ObjectBar Skin |
| obu | WindLDR Device Data List |
| obx | IBM Rational XDE Object File |
| obx | pCon.planner Pro OBX Exchange Format Data |
| oc | MODFLOW Output Control Data |
| oc3 | OpenCanvas 3 Event |
| oc4 | OpenCanvas 4 Event |
| oc5 | OpenCanvas 5 Event |
| oc8 | OrgCon 8 Organization Data |
| oc9 | OrgCon 9 Organization Data |
| ocb | DOpus Configuration Backup |
| occ | DB/TextWorks List of BTX Records |
| occ | OptControlCentre Model |
| ocd | OCAD Map |
| ocen | EdGCM OCEN Data |
| ocf | Object Craft File |
| ocf | Orbit Construction Data |
