| ocp | Orbit Composite Point Cloud |
| ocr | Orbit Composite Resources Data |
| ocs | OCS Inventory NG Data |
| ocsmeet | Microsoft Lync Online Meeting Data |
| ocsp | HAProxy OCSP Data |
| oct | Radiance Octree |
| ocv | Optical Character Verification Data |
| ocw | Symantec ESM Oracle Configuration Watch Template |
| oc_ | Compressed OCX File |
| od | Atari Jaguar DSP Object Module |
| od | Atari Jaguar Envelope Definition Data |
| od | Atari Jaguar Sound Patch |
| od | Mascopt Data |
| od1 | Omnis Studio Database |
| od2 | Omnis Studio Database |
| od3 | Omnis Studio Database |
| od4 | Omnis Studio Database |
| od5 | Omnis Studio Database |
| od6 | Omnis Studio Database |
| od7 | Omnis Studio Database |
| od8 | Omnis Studio Database |
| od9 | Omnis Studio Database |
| oda | AIBO ODA File |
| odat | Hopsan Optimization Data |
| odb | Abaqus/CAE Binary Output Data |
| odb | Abaqus/Explicit Output Database |
| odc | Microsoft Office Database Connection Data |
| ode | XPP ODE Unit |
| odf | ADS40 Orientation Data |
| odh | Odigo Messenger History Data |
