File extensions that begin with O.
Ext. Type of file
O Unix machine language
OAZ OAZ Fax
OBD Microsoft Office binder
OBJ Machine language
OBJ Wavefront 3D
OBZ Microsoft Office wizard
OCX ActiveX control (OLE control)
ODF OpenDocument formulas
ODG OpenDocument graphics
ODP OpenDocument presentations
ODS OpenDocument spreadsheet
ODT OpenDocument text
OEB Open eBook publication
OGA Ogg audio
OGG Ogg Vorbis audio
OGM Ogg video (early)
OGV Ogg video
OGX Ogg mixed
OLB OLE object library
OLE OLE object
ONE OneNote file
OPF EPUB metadata
OPS EPUB publication
ORG Organizer
OSP OpenShot Project
OST Outlook cached data
OTF OpenType font
OTT Apache OpenOffice template
OVD ObjectVision application
OVL Overlay module
OVR Overlay module
OUT CDE accumulated definitions
OZM Sharp Organizer memo bank
OZP Sharp Organizer telephone bank