File types with extensions that start with the letter O

File Extention	File Type	Description
.o	Developer	Compiled Object File
.oab	Data	Offline Address Book
.oam	Web	Adobe Edge Animate Widget File
.oar	Compressed	OpenSimulator Archive
.ob!	Misc	Orbit Downloader Incomplete Download
.obb	Data	Android Opaque Binary Blob File
.obd	Data	Office Binder Document
.obi	Settings	Outlook RSS Subscription File
.obj	Data	Relocatable Object Code
.obj	3D Image	Wavefront 3D Object File
.obk	Backup	Backup File
.obml	Web	Opera Mini Saved Web Page
.obp	3D Image	Bryce Object File
.obt	Settings	Openbox Theme File
.obw	Audio	Superior Drummer Sounds File
.obz	3D Image	Compressed 3D Object File
.oc3	Raster Image	openCanvas 3 Event File
.oc4	Raster Image	openCanvas 4 Event File
.oc5	Raster Image	openCanvas 5 Event File
.oca	Developer	Custom Control Library Type File
.occ	Data	Oceanic DataPool File
.ocd	GIS	OCAD Map File
.oce	Settings	Open Catalog Extension Connection File
.oci	Raster Image	openCanvas Image
.ocr	Misc	Subtitle Workshop OCR Script
.ocr	Text	FAXGrapper Fax Text File
.oct	3D Image	Radiance Octree File
.octest	Developer	Xcode Objective-C Unit Test Bundle
.ocx	Developer	ActiveX Control
.od	Data	Mascopt Graph Request File
.odb	Database	OpenDocument Database
.odb	Database	ABAQUS Database
.odc	Data	OpenDocument Chart File
.odc	Settings	Office Data Connection File
.odf	Game	Battlezone Object Definition File
.odf	Misc	OpenDocument Formula
.odf	Data	Open Document File
.odg	Vector Image	OpenDocument Graphic File
.odi	Raster Image	OpenDocument Image
.odif	Text	Open Document Interchange Format
.odl	Developer	Object Description Language File
.odm	Audio	OverDrive Media File
.odm	Text	OpenDocument Master Document
.odo	Text	Online Operating System Write Document
.odp	Data	OpenDocument Presentation
.ods	Misc	Outlook Express 5 Mailbox
.ods	Spreadsheet	OpenDocument Spreadsheet
.odt	Text	OpenDocument Text Document
.odx	Data	BizTalk Server Orchestration File
.oeaccount	Data	Windows Mail Account File
.oeb	eBook	Open eBook File
.oeb	Backup	Outlook Express Backup Wizard File
.oem	Settings	OEM Setup File
.oem	Data	OEMEdit Save File
.oex	Plugin	Opera Extension
.ofc	Data	Open Financial Connectivity File
.off	3D Image	Object File Format
.officeui	Settings	Microsoft Office UI Customization File
.ofl	Text	Ots File List
.ofm	Data	Melco Embroidery File
.ofm	Data	OmniForm Form
.ofr	Misc	SMS Offer Manager File
.ofr	Audio	OptimFROG Audio File
.oft	Data	Outlook File Template
.ofx	Data	Open Financial Exchange File
.oga	Audio	Ogg Vorbis Audio File
.ogf	3D Image	S.T.A.L.K.E.R. Model File
.ogg	Audio	Ogg Vorbis Audio File
.ogm	Video	Ogg Media File
.ognc	Web	Dynamic Web Page
.ogs	Data	Origons Movie Data File
.ogv	Video	Ogg Video File
.ogx	Video	Ogg Vorbis Multiplexed Media File
.ogz	Game	Cube 2 Map File
.okt	Audio	Oktalyzer Module
.ol	3D Image	Valve Hammer Object Layout File
.ola	Page Layout	Online Access File
.olb	Misc	OLE Object Library
.olb	CAD	OrCAD Symbol Library File
.old	Backup	Backup File
.olk	Data	Outlook Address Book File
.olk14category	Data	Outlook Category File
.olk14contact	Data	Outlook Contact File
.olk14event	Data	Outlook Calendar Event File
.olk14group	Data	Outlook Group File
.olk14mailaccount	Data	Outlook Mail Account File
.olk14message	Data	Outlook Message File
.olk14msgsource	Data	Outlook Email Message Data File
.olk14note	Data	Outlook Note File
.olk14pref	Settings	Outlook Preferences File
.olk14signature	Data	Outlook Signature File
.olk14task	Data	Outlook Task File
.olm	Data	Mac Outlook Database File
.olp	Web	Office Live Package
.olt	Data	Orbit Downloads List
.oma	Audio	Sony OpenMG Music File
.omcs	Data	Office Manager Access File
.omf	Raster Image	OMF Interchange Image File
.omf	Audio	Open Media Framework File
.omg	Audio	OpenMG Audio File
.omg	Disk Image	Image File
.omo	Developer	OMake Object File
.omod	Game	Oblivion Mod Archive
.omp	Data	Office Manager Document Archive
.omx	Audio	OtsAV Media Library Information File
.ond	Data	Lotus Notes Encapsulated Memo File
.one	Data	OneNote Document
.onepkg	Backup	Microsoft OneNote Package File
.onetoc2	Settings	Microsoft OneNote Table of Contents File
.ont	Data	theWord Bible Text Module
.ontx	Data	theWord Encrypted Bible Text Module
.oo3	Data	OmniOutliner 3 File
.ook	Misc	Arachne Batch Script
.op	Data	OpenPAT Report
.op2	Data	Nastran Output File
.op4	Data	Nastran Output File
.opal	Data	Microsoft Office User Settings File
.opax	Data	Microsoft Office User Settings File
.opd	Page Layout	OmniPage Document
.opd	Data	Durango Document
.opdownload	Misc	Opera Partially Downloaded File
.openbsd	Text	OpenBSD Readme File
.opf	eBook	Open Packaging Format File
.opf	Misc	FlipAlbum File
.opf	Data	FlipViewer FlipBook File
.opj	CAD	OrCAD Project File
.oplc	Raster Image	Nokia Operator Logo File
.opml	Web	Outline Processor Markup Language File
.ops	Settings	Office Profile Settings File
.opt	CAD	Opterecenja File
.opt	Settings	Options File
.options	Settings	SE-SOFT Configuration File
.opts	Settings	Linux Configuration Options File
.opus	Audio	Opus Audio File
.opx	Data	FlipAlbum Photo Album File
.opx	Data	OrgPlus Org Chart
.oqy	Database	Excel OLAP Query File
.or2	Data	Lotus Organizer 2 File
.or3	Data	IBM Lotus Organizer 97 File
.or4	Data	IBM Lotus Organizer 97 GS File
.or5	Data	Lotus Organizer 5 File
.or6	Data	Lotus Organizer 6 File
.ora	Database	Oracle Database Configuration File
.ora	Raster Image	OpenRaster Image File
.orc	Audio	Voyetra Digital Orchestrator File
.orderedtest	Developer	Visual Studio Ordered Test File
.ore	Executable	Ore Executable File
.orf	Camera Raw	Olympus RAW File
.org	Data	Lotus Organizer File
.ori	Backup	Original File
.orig	Backup	Original File
.ort	Text	Rich Text Editor Document
.orv	Video	Oracom Video File
.orx	Database	RadiantOne VDS Database Schema
.os	Developer	ObjectScript Source File
.osax	Plugin	AppleScript Scripting Addition
.osb	GIS	OpenStreetMap Binary Map File
.osc	Developer	Obix Source Code File
.osc	GIS	OpenStreetMap Change File
.osdx	Settings	Search Connector Description File
.osk	Game	Osu! Skin File
.osm	GIS	OpenStreetMap Map File
.osp	Video	OpenShot Project File
.osr	Game	Osu! Replay File
.oss	Settings	Microsoft Outlook Saved Search File
.ost	Misc	Outlook Offline Folder File
.osu	Game	Osu! Script
.osx	Executable	PowerPC Executable File
.osz	Game	Osu! Beatmap File
.osz	Data	OpenLP Service File
.ot	Data	theWord Old Testament Text Module
.ota	Raster Image	OTA Bitmap Image
.otb	Raster Image	Nokia Over The Air Bitmap Image
.otc	Misc	OpenDocument Chart Template
.otf	Data	OpenTuft Tufting Design File
.otf	Misc	OpenDocument Formula Template
.otf	Font	OpenType Font
.otg	Vector Image	OpenDocument Graphic Template
.oth	Web	OpenDocument HTML Template
.oti	Raster Image	OpenDocument Image Template
.otl	Data	NoteTab Outline File
.otln	Data	Opal Outline File
.otm	Executable	Outlook Macro File
.otp	Data	OpenDocument Presentation Template
.otrkey	Video	OnlineTvRecorder Encoded Video File
.ots	Audio	OtsAV Album File
.ots	Spreadsheet	OpenDocument Spreadsheet Template
.ott	Text	OpenDocument Document Template
.otx	Data	theWord Encrypted Old Testament Text Module
.otz	Settings	OpenLP Theme File
.out	Executable	Compiled Executable File
.out	Data	Output File
.ov2	GIS	TomTom Points of Interest Database
.ova	Data	Octava Musical Score
.ova	Data	Open Virtual Appliance
.ove	Audio	Overture Musical Score
.ovf	Data	Open Virtualization File
.ovh	Game	OMSI Vehicle Configuration File
.ovl	Game	Rollercoaster Tycoon 3 Data File
.ovp	Vector Image	The Overlay Maker Package File
.ovpn	Settings	OpenVPN Configuration File
.ovr	Vector Image	The Overlay Maker Overlay File
.ovw	Audio	Logic Pro Overview File
.ovw	Audio	Cubase WAVE Overview File
.ow	Developer	Free Pascal 1.0.x Object File
.owc	Database	OutWit Catch Database
.owg	Misc	OutWit Gear Database
.owl	Developer	OWL Source Code File
.owm	Misc	OutWit XML Mashup File
.oxps	Page Layout	OpenXPS File
.oxt	Plugin	Apache OpenOffice Extension
.oxygene	Developer	Oxygene Project File
.oyx	Backup	Approach Alternate Database Index
.oz	Compressed	Opera Job Management Compressed File
.ozb	Raster Image	MU Online Image File
.ozj	Raster Image	MU Online Image File
.ozt	Raster Image	MU Online Image File