| otl | Ventura Publisher Type Foundry Outline Editor Data |
| otlb | Microsoft OLE Type Library |
| otn | OmniPage Training |
| otodot | OTOsuite Custom Report Data |
| otoset | OTOsuite Settings Data |
| otp | Top Secret Crypto Gold One Time Pad Key |
| otr | IRIX Compiled File-type Rules Data |
| otv | Rotor-Disc OTV Kit OTV Calibration Data |
| otv5key | onlineTV Registration Key Data |
| otvdatafile | onlineTV Data |
| otvlangfile | onlineTV Language Data |
| otx | theWord Encrypted Old Testament Text Module |
| otz | OpenLP Theme File |
| oub | Oubliette Data |
| oud | Adlib Express User Defined Dictionary |
| ouf | Otravi Unit Frames Data |
| out | Altair FEKO POSTFEKO ASCII Output Data |
| out | BibExcel OUT Data |
| out | Catapult DCT2000 Trace Data |
| out | FAST Output Data |
| out | Fire Dynamics Simulator Output Data |
| out | Movie.BYU Output Data |
| out | MyInfo Document Outline Data |
| out | Nastran Tabular Output |
| out | NovaBACKUP Backup Data |
| out | RMCProfile Results Data |
| out1 | UltraEdit Outline Data |
| outb | FAST Binary Output Data |
| outjob | Altium Designer OutputJob Data |
| outline | FontTwister Letter Outline Data |
| ouv | Sphinx Open Ended Responses Data |
| oux | BibExcel OUX Data |
| oux | PCCharge Transaction Response XML File |
| ov | OpenInsight Overflow Data |
| ov1 | MS-DOS Overlay Data |
