| R | Resource file |
| R8 | Raw graphics (One byte per pixel) plane one (PicLab) |
| R8P | Pcl 4 bitmap font (Intellifont) |
| RA | RealMedia streaming audio file |
| RAD | Radar data file (Radar ViewPoint) |
| RAM | RealMedia metafile |
| RAO | ReadAllOver (YOUniverse) |
| RAR | WinRAR Compressed Archive |
| RAS | Bitmap (Sun Raster Images) |
| RAT | Datafile (RATS) |
| RAV | Norton Antivirus file |
| RAW | Raw signed PCM data |
| RBF | Windows Installer rollback file |
| RBH | Maintained by RoboHELP, the RBH file adds to the information contained in the Help project file |
| RC | Resource script (Borland C++) |
| RCG | Newsgroup file (Netscape) |
| RD1 | Registered level file (Descent1) |
| RDF | Compiled UIC source code (Geoworks UI Compiler) |
| RDI | Device-independent bitmap file |
| RDL | Registered Level file (Descent) |
| RDX | Datafile (Reflex) |
| RDZ | RemoteDocs compressed and encrypted file |
| REC | Recorded macro (Microsoft Windows 3.x) |
| RED | Path information file (Clarion Modula-2) |
| REF | Reference file (Generic) |
| REG | Registration file (Corel) |
| REM | Remarks file (Generic) |
| REP | Report file (Visual dBase) |
| REQ | Request file (Generic) |
| RES | Compiled resource file (Borland C++) |
| REV | Revision file (GeoWorks) |
| REX | Report definition (Oracle) |
| REZ | Resource file for the Lithtech game engine |
| RF | Raster graphics file (Sun) |
| RFT | Revisable Form Text (part of IBM's DCA or Document Content Architecture) |
| RGB | Silicon Graphics image file |
| RGX | Symbol tables (ReaGeniX code generator) |
| RH | Resource header file (Borland C++ 4.5) |
| RI | Data file (Lotus 1-2-3) |
| RIB | Graphics in Renderman format (3DReality) |
| RIC | Fax document (Ricoh) |
| RIF | Image file (Metacreations Painter 5) |
| RIP | Error file for Lotus Notes |
| RIX | Bitmap graphics (ColorRIX VGA Paint) |
| RL1 | Regestered level file (Descent1) |
| RL2 | Registered level file (Descent2) |
| RL4 | Bitmap graphics file |
| RL8 | Bitmap graphics file |
| RLA | Wavefront raster image (SDSC Image Tool) |
| RLB | Data file (Harvard Graphics Win 9.x) |
| RLC | Graphics file (1 bit per pixel scanner output file) |
| RLE | Run-Length Encoded bitmap (SDSC Image Tool) |
| RLZ | Realizer source code file (CA-Realizer) |
| RM | Video file (RealAudio) |
| RMB | RegistryMaster branch |
| RMD | Document (Microsoft RegMaid) |
| RMF | Rich music format (Beatnik) |
| RMI | MIDI music |
| RMK | Makefile (Clipper RMake) |
| RMVB | RealVideo Variable Bit Rate File |
| RN | Xpl Program file (Nota Bene) |
| RND | Rendering slide (AutoCAD-AutoShade) |
| RNO | Runoff file (VAX) |
| ROL | FM music Adlib Music file (Roland) |
| ROM | Cartridge-based home video game emulator file (exact copy of ROM contents in cartridges from Atari 2600, Colecovision, Sega, Nintendo, etc.; not interchangeable between emulators) |
| ROQ | Id software game file |
| ROV | Data file (Rescue Rover) |
| RPD | Database (RapidFire) |
| RPL | Video file (Tomb Raider) |
| RPM | Package Manager (RedHat Linux) |
| RPS | Borland Translation Repository |
| RPT | Crystal Reports file ( and a sub-set of Microsoft Visual Basic) |
| RRS | Saved game file (Ace Road Rash) |
| RS | Datafile (Amiga Resource Reassembler) |
| RS_ | Resource fork file (Macintosh Mac-ette) |
| RSB | Red Storm bitmap (Rainbow 6 (Game) and several image editing programs) |
| RSC | Resource file (Generic) |
| RSL | Paradox 7 reports (Broderland) |
| RSM | Resume file |
| RSP | Response file (Generic) |
| RTC | Rich Text Compressed file |
| RTF | Help file script (Microsoft Windows 9.x) |
| RTK | Used by RoboHELP to simulate the search feature of Windows help |
| RTL | Text file (Generic) |
| RTM | Music module (MOD) (Real Tracker) |
| RTP | Software update package data file (RTpatch) |
| RTS | Runtime library file (CA-Realizer) |
| RUL | Extension used in InstallShield |
| RUN | Compiled output p-code file (Softworks basic compiler) (SoftworksLtd) |
| RVP | Scan Configuration file (MIME) (Microsoft) |
| RVW | Review file (Generic) |
| RWS | Resource Workshop data file (Borland C++) |
| RWX | Script file (RenderWare) |
| RXX | RAR compressed files from a multi-volume archive (xx = a number from 01 to 99) |
