.OAZ - OAZ Fax Manager

.OBD - Microsoft Office Binder (file extension).

.OBJ - Object module (file extension).

.OCX - Object Linking and Embedding (OLE) Custom Control (filename extension).

.ODF - Open Document Interchange (ODIF) (filename extension).

.OLB - AUTOGEN.

.OLE - Object Linking and Embedding OLE object (file extension).

.OMA - Sony OpenMG Music Format File (Sony Corporation of America).

.ONX - Onyx Graphics Postershop (filename extension).

.ORI - Original

.OVL - Overlay module

.OVR - Overlay module

.OZM - Sharp Organizer memo bank