| Extension | File Type | Files scanned | Contributor |
| X | Microsoft Direct3D Object (binary) | 33 | |
| X | Microsoft Direct3D Object (txt) | 31 | |
| X3D | X3D file | 16 | |
| X3F | Sigma - Foveon X3 raw picture | 7 | |
| X64 | X64 and VICE emulators disk image | 2 | |
| XA | Maxis XA Audio (music) | 2 | |
| XA | Maxis XA Audio (sound/speech) | 2 | |
| XADML | XML-Based Application Description Information | 100 | |
| XAML | Microsoft Extensible Application Markup Language | 22 | |
| XAML | Microsoft Extensible Application Markup Language (Unicode) | 12 | |
| XAR | XAR archive | 2 | |
| XAR | Xara drawing | 14 | |
| XBE | XBOX executable | 3 | |
| XBK | SMART Board Slide Collection | 10 | |
| XCF/GZ | The GIMP image | 7 | |
| XCR | XCR archive | 2 | |
| XDD | XFIT XDD format data file | 8 | |
| XDR | XML-Data Reduced | 23 | |
| XDW | DocuWorks File | 11 | |
| XEB | Apabi eBook | 2 | |
| XEX | XeX file | 3 | |
| XFB | Binary Device Interface File Format | 4 | |
| XFD | Acu4GL/AcuCOBOL Extended File Descriptor | 7 | |
| XFDL | XFDL form | 19 | |
| XFM | Syntrillium Cool Edit Transform Effect | 89 | |
| XGR | GraphEdit Filter Graph Markup Language | 5 | |
| XI | eXtended Instrument (generic) | 10 | |
| XIF | Text Device Interface File Format | 9 | |
| XIP | Hotbar skin | 14 | |
| XKS | IBM Softcopy Reader PDF Extended bookshelf file | 12 | |
| XLF | XLIFF - XML Localization Interchange File Format | 5 | |
| XLF | XLIFF - XML Localization Interchange File Format | 4 | |
| XLO | Autodesk Inventor Export Journal | 10 | |
| XLR | Microsoft Works Spreadsheet | 39 | |
| XLS | Microsoft Excel sheet | 1046 | |
| XLS | Microsoft Excel sheet (alternate) | 9 | |
| XLS | Microsoft Excel sheet (older format) | 123 | |
| XLSX | Excel Microsoft Office Open XML Format document | 6 | |
| XLT | Biew Xlat Table | 16 | |
| XM | Fast Tracker 2 Extended Module | 7 | |
| XMCD | Mathcad XML based worksheet | 32 | | NEW! |
| XMCD | XMCD CD information | 2 | |
| XMFG | MediaForge Runtime Player Distribution Project | 8 | |
| XMI | XMI - XML Metadata Interchange | 13 | |
| XMI | XMill compressed XML | 24 | |
| XML | Android Manifest | 11 | |
| XML | Artweaver Brush | 212 | |
| XML | COLLADA interchange database scheme for 3D | 19 | |
| XML | Generic XML (ASCII) | 2 | |
| XML | Gunz Online NPC model | 9 | |
| XML | HP printer usage data | 11 | |
| XML | MSN Messenger log | 34 | Renan (aka "Wizard") |
| XML | Microsoft BizTalk XML message | 3 | |
| XML | MusicXML | 33 | |
| XML | NewsML file | 15 | |
| XML | Out-Of-Box Experience file | 4 | |
| XML | Portable Application Description (PAD) | 20 | |
| XML | Portable Application Description (UTF-8) (PAD) | 14 | |
| XML | QTI document | 17 | |
| XML | ROR website description | 21 | |
| XML | SmartFTP transfer queue | 3 | |
| XML | TestGen XML data | 6 | |
| XML | TfID - Text File IDentifier definition (v0.x) | 55 | |
| XML | TrID definition! :-) | 1554 | |
| XML | ZipGenius configuration | 4 | |
| XML | ksudoku puzzle | 8 | |
| XML | m0n0wall configuration | 6 | |
| XML/ATOM | Atom web feed | 13 | |
| XML/RSS | RSS web feed | 12 | |
| XMOD | Monarch Pro model | 26 | |
| XMP | Adobe Extensible Metadata Platform | 7 | |
| XNK | Microsoft Exchange Server Shortcut | 17 | |
| XPF | X-Protector Project File | 6 | .Cryorb |
| XPF | XaoS Position File | 6 | |
| XPI | Mozilla Firefox browser extension | 127 | |
| XPL | X-Plane plugin | 20 | |
| XPM | X PixMap bitmap | 14 | |
| XPR | Creature House Expression3 drawing | 13 | |
| XPS | MonkeyJam Exposure Sheet | 2 | |
| XPS | XML Paper Specification | 63 | |
| XPT | SAS Transport (XPORT) format | 22 | |
| XPT | XPCOM Type Library | 251 | Roberto 'rbnet' Bolli |
| XRC | wxWindows - wxPython Resource File | 4 | |
| XRM-MS | Microsoft security certificate | 7 | |
| XRM-MS | Microsoft security certificate (Unicode) | 9 | |
| XS3/XS4/XS5 | XESS worksheet (generic) | 26 | |
| XSD | XML Schema | 16 | |
| XSI | SoftImage XSI 3D model | 4 | |
| XSN | InfoPath Dynamic Form - Template | 25 | |
| XSPF | XML Shareable Playlist Format | 8 | |
| XTC | XTrkCAD project | 34 | |
| XTC | XTrkCAD project (with rem) | 34 | |
| XTG | QuarkXPress Tags file | 19 | |
| XTP | XTrkCAD parameters | 73 | |
| XTR | XTrkCAD demo | 76 | |
| XTR | XTrkCAD demo (with rem) | 29 | |
| XUL | Mozilla XML User interface Language | 6 | |
| XWB | Xbox Wavebank audio data | 3 | |
| XWD | X Windows Dump bitmap | 44 | |
| XWF | Declan Software word file | 12 | |
| XWS | Xara WebStyle file | 9 | |
| XXX | Compucon/Singer PSW Embroidery Design File | 6 | FILExt |
| XYZ | XYZ Graphics bitmap | 2 | |
| XZP | XZP container format | 3 | |
| X_T | Modeller transmit file | 11 | |
