| S | Assembler Source Code |
| S$$ | Temporary Sort File |
| S01 | WordPerfect Distribution File |
| S02 | WordPerfect Distribution File |
| S03 | WordPerfect Distribution File |
| S19 | Motorola EEPROM Programming |
| S2P | Sonnet File |
| S31 | Scream Tracker v3 Instrument |
| S3D | Micrografx Simply 3D Project |
| S3D | EverQuest File |
| S3I | ScreamTracker v3 Instrument |
| S3M | ScreamTracker v3 Module |
| S3M | ScreamTracker v3 Sound File |
| SA6 | Street Atlas 6.0 |
| SA8 | Street Atlas File |
| SAC | Adobe Shared Asset Catalog |
| SAD | Serveron Analyzer Data File |
| SAD | Electronic Arts Black & White Game Sound File |
| SAF | MusicMatch Jukebox Secure Audio File |
| SAH | SETI@Home Data File |
| SAL | SQL Application Language |
| SAL | SoriTec Database |
| SAM | Ami Pro Text File |
| SAM | Signed 8-bit Sample Data |
| SAM | Microsoft Office 97 File Converter |
| SAM | Map File |
| SAN | The Curse of Monkey Island Movie File |
| SAS | Used by SAS version 6.03 |
| SAT | ACIS Solid Model (any ACIS-based CAD program) |
| SAV | Saved File (various) |
| SB | Raw Signed Byte (8-bit) Data |
| SB | Audio File |
| SBI | Creative Labs SoundBlaster Instrument |
| SBJ | Micrografx Clipart or Palette Index |
| SBK | Asymetrics ToolBook System Book |
| SBK | Emu SoundFont v1.x Bank Files |
| SBK | Creative Labs Soundfont 1.0 Bank File |
| SBL | Shockwave Flash Object |
| SBP | Super-Base 4 Database Program |
| SBP | IBM Storyboard Image |
| SBR | Source Browser for BSCMAKE |
| SBT | SuperBase 4 Database Text |
| SBX | Adobe Illustrator Tsume |
| SC | Paradox Source Code |
| SC | Framework Screen Driver |
| SC | Ingres Embedded SQL/C Source File |
| SC2 | Microsoft Schedule+ 7 File Format |
| SC2 | SimCity 2000 City |
| SC2 | SAS Catalogue |
| SC2 | II PC Instrument |
| SC3 | Harvard Screen Driver |
| SC3 | SimCity 3000 File |
| SC3 | dBase Screen Mask File |
| SC4 | RollerCoaster Tycoon Scenario |
| SCB | Corel WordPerfect 8 Scrapbook Image |
| SCC | Microsoft Source Safe File |
| SCC | Stamp Collector's Girl Friday Catalog File |
| SCD | Microsoft Schedule+ 7 |
| SCD | Graphic (SCODL Scan Conversion Object Description Language) |
| SCD | TurboTax Schedule File |
| SCE | SoftCuisine Data Exchange File |
| SCF | Windows Explorer Command File |
| SCF | Score Maker Presentation |
| SCH | Microsoft Schedule+ File |
| SCH | ORCAD Vector Drawing Schematic |
| SCH | EAGLE Schematic File |
| SCI | Sci-Fax Document |
| SCI | ColoRIX Image |
| SCI | ScanVec Inspire File |
| SCI | System Configuration Data |
| SCL | SCALA Scale |
| SCM | Lotus ScreenCam Movie |
| SCM | SchematicMaker (Topanga Software) File |
| SCM | ICQ Sound Compressed Sound Scheme |
| SCM | Starcraft Map File |
| SCN | Visual Basic |
| SCN | Cobol |
| SCN | TrueSpace2 Scene |
| SCN | Compressed Screen Format |
| SCN | Scenario File For Many Games |
| SCO | High Score (various) |
| SCP | Script (various) |
| SCP | ColorRIX Image |
| SCR | Windows Screensaver |
| SCR | Faxview Fax |
| SCR | Procomm Plus Screen Snapshot File |
| SCR | Script (various) |
| SCR | LocoScript Screen Font File |
| SCS | Lotus ScreenCam Script |
| SCT | Scitex Continuous Tone Bitmap |
| SCT | Microsoft FoxPro Forms |
| SCT | Windows Script Component |
| SCT | PC Tools Script Tools |
| SCT | SAS Catalog |
| SCT | Lotus Screen Capture Text |
| SCU | ColorRIX Image |
| SCV | ScanVec CASmate File |
| SCX | MS FoxPro Screen File |
| SCX | ColorRIX Image |
| SCX | Starcraft Map File |
| SCX | Microsoft Class Browser Form |
| SCX | Stanford Chart |