| SND | NeXT Sound |
| SND | Macintosh Sound Resource |
| SND | Raw Unsigned PCM Data |
| SND | AKAI MPC-series Sample |
| SND | Sound Clip (various) |
| SNG | Midisoft Studio Sound |
| SNM | Netscape Folder Cache |
| SNO | SNOBOL 4 Source Code |
| SNP | Microsoft Access 97 Report Snapshot |
| SNX | QuickBooks Data |
| SNX | StarCraft Saved File |
| SO | UNIX Shared Library |
| SOA | Sage MAS 90 Accounting Software File |
| SOB | Visual Basic |
| SOM | Paradox Sort Information |
| SOM | Quattro Pro Network Serial Numbers |
| SON | SBStudio II Song |
| SOU | SB Studio II Sound |
| SP | UNIX Splint Archive |
| SPC | Atari Spectrum |
| SPC | Multiplan Program |
| SPC | WordPerfect Temp File |
| SPC | SNES Audio file |
| SPD | Bitstream Speedo Scalable Font |
| SPD | PostScript Printer Description |
| SPD | Speech Data File |
| SPD | Mini-driver |
| SPD | Harvard Bitstream Typefaces |
| SPF | EnerGraphics Presentation |
| SPG | Sprint Glossary |
| SPI | Philips, Siemens Scanners Image |
| SPL | Shockwave Flash Object |
| SPL | Splint Archive |
| SPL | Digitracker Sample |
| SPL | Printer Spool File |
| SPL | Sprint Printer Driver |
| SPL | Spell Checker |
| SPM | WordPerfect File |
| SPN | WordPerfect Distribution File |
| SPP | Sprint Printer File |
| SPP | Serif PhotoPlus Native Format File |
| SPR | FoxPro Screen Program |
| SPR | Sprite (various) |
| SPR | Sprint Document Letter |
| SPS | SPSS source Code |
| SPS | Sprint Screen Driver |
| SPT | SPITBOL Source Code |
| SPW | Jandel Sigma Stat Statistical Advisor |
| SPW | Sigma-Plot Spreadsheet |
| SPX | FoxPro Compiled Program |
| SPX | SPITBOL |
| SQB | SyQuest Backup |
| SQC | Structured Query Language Common Code File |
| SQD | Squish Message Data |
| SQI | Squish Message Data Index |
| SQL | Structured Query Language Data |
| SQR | Structured Query Language Program File |
| SQZ | Squeeze Archive |
| SR | Sun Raster Image |
| SRB | Corel ClipArt ScrapBook |
| SRC | Source code (various) |
| SRF | Sun Raster Graphic File |
| SRL | Medical Drug Reference Search Results |
| SRQ | Microsoft Server Request File Unprocessed |
| SRS | Sun Raster File Image |
| SRS | Microsoft Server Request File Partially Processed |
| SS | Splash Image |
| SSC | SourceSafe (source code control) Configuration |
| SSD | SAS database |
| SSF | Enable Spreadsheet File |
| SSH | Style Sheet for Microsoft Internet Explorer |
| SSI | Installer/GD Software Setup Information |
| SSL | Corel Smart Library (Corel Flow) |
| SSM | RealPlay Standard Streming Metafile |
| SSS | Studio Session Song |
| SST | Certificate Store |
| ST | Small Talk Source Code |
| ST | NeoPaint Stamp File |
| ST | Atari ST Disk Image |
| STA | Eudora File |
| STB | Genus Stub Library |
| STD | State Transition Diagram Graphic |
| STD | SureThing CD Labeler Document |
| STD | LocoScript Standard Script File |
| STF | Lotus Agenda |
| STF | Shrink-to-Fit Archive |
| STF | Structured File (various) |
| STF | Setup Information (various) |
| STG | PageKeeper Storage File |
| STI | Symbol and Type Information for Portable Executable Program |
| STK | Personal Stock Monitor File |
| STL | C++ Standard Template Library |
| STL | Certificate Trust List |
| STL | CAD Software Solid Modeling/Prototyping File |
| STL | Macromedia Fireworks Style Library |
| STM | HTML Form |
| STM | Scream Tracker v2 Music Module |
| STM | State Transition Diagram Model |
| STM | PhotoStudio Stamp |
| STM | Sound File |
| STO | Genus Pascal Stub OBJ File |
| STP | PageKeeper Packed Storage File |
| STR | dBase Structure List |
| STR | DataPerfect Structure File |
| STR | Sceensaver |
| STR | Stream File (Playstation Discs) |
| STS | MS C Project Status Info |
| STT | Automap Template |
| STX | CA-Simply Tax |
| STX | SmarText Electronic Book Document |
| STY | Microsoft Word for DOS Style Sheet |
| STY | Micrografx Picture Publisher Print Style |
| STY | Ventura Publisher Style Sheet |
| STY | MS Interactive Music Control |
| STY | LaTeX2e Style |
| SUB | CloneCd Related File |
| SUB | Divx Subtitles |
| SUD | Super Project Analyzer Data |
| SUM | Summary (various) |
| SUN | SUN Raster Image |
| SUP | Error Suppression for Nu-Mega Technologies, Inc. BoundsChecker |
| SUP | WordPerfect Supplemental Dictionary |
| SUP | Apple Macintosh StartupScreen |
| SV$ | AutoCAD Autosave File |
| SV1 | Transport Tycoon Saved Game |
| SV4 | RollerCoaster Tycoon Saved Game |
| SVD | Word Backup File |
| SVG | Word Backup File |
| SVG | Scalable Vector Graphics File |
| SVH | Black Diamond Consulting (Surround Video - Animated Internet Picture) |
| SVR | SuperScape ActiveX Superscape Viscape Control |
| SVS | Word Backup File |
| SVX | Amiga 8SVX Sound |
| SVX | Interchange File Format, 8SVX/16SV |
| SW | Raw signed Word (16bit) Data |
| SW | Audio File |
| SWA | Shockwave Audio File |
| SWD | Storybook File |
| SWF | Shockwave Flash Object |
| SWF | Microsoft Sidewinder Profile Activator |
| SWI | Swish Data File |
| SWL | Macromedia Flash Format |
| SWP | Windows Swap File |
| SWP | DataCAD Swap File |
| SWP | Borland Sprint Backup |
| SWT | VB Setup Wizard Template File |
| SWT | Space Watch Pro Data File |
| SWT | Macromedia Authoring Flash File |
| SXW | Staroffice Word Document |
| SY1 | Ami Pro Smartpix Symbol Library |
| SY3 | Harvard Graphics 3.x Symbol |
| SYD | Sysedit Backup File |
| SYL | SYLK Spreadsheet Format |
| SYM | Symbol Table (various) |
| SYM | Harvard Graphics 2.x |
| SYM | Borland C++ Precompiled Headers |
| SYN | Synonym File |
| SYS | System Configuration |
| SYS | System Device Driver |
| SYW | Yamaha SY-series Wave Files |
| SYW | Harvard Symbol Graphic |