| Extension | 描述 | 檔案格式 |
|---|
| x | DirectX Object File | 3D Files |
| x32 | Adobe Xtra File | 3D Files |
| x64 | Commodore 64 Disk Image File | 磁碟映像檔 |
| xap | Silveright Application Package | 網頁檔案 |
| xbel | XML Bookmark Exchange Language File | 網頁檔案 |
| xcf | Gimp Image File | 圖檔 |
| xdw | X Windows Screen Dump File | 圖檔 |
| xex | Xbox 360 Executable File | 執行檔 |
| xfdl | Extensible Forms Description Language File | 網頁檔案 |
| xhtml | Extensible HyperText Markup Language File | 網頁檔案 |
| xlr | Microsoft Works Spreadsheet File | 試算表檔案 |
| xls | Excel Spreadsheet File | 試算表檔案 |
| xlsm | Microsoft Excel Macro-enabled Workbook file | 試算表檔案 |
| xlsx | Microsoft Excel XML File | 資料檔 |
| xmcd | Mathcad Worksheet File | 遊戲檔案 |
| xmf | Gamejack Disk Image File | 磁碟映像檔 |
| xml | Extensible Markup Language | 資料檔 |
| xmp | Extensible Metadata Platform | Misc Files |
| xp3 | TVP XPK3 Virtual File System File | 遊戲檔案 |
| xpi | XPInstall File | 壓縮檔案 |
| xps | XML Paper Specification File | Layout Files |
| xpt | Mozilla Firefox Component File | 網頁檔案 |
| xs | Age Of Empires III Map AI Generator File | 遊戲檔案 |
| xsd | XML Schema File | Developer Files |
| xspf | XML Shareable Playlist File | 聲音檔案 |
| xtm | Xtremsplit Data File | 資料檔 |
| xtreme | Winstep Theme Pack File | Misc Files |
| xul | XML User Interface Language File | Developer Files |
| xv | Khoros VIFF Bitmap File | 圖檔 |
| xvid | Xvid Video File | 視頻檔案 |
| xxx | Singer Embroidery File | Misc Files |
| xz | XZ Compressed Archive | 壓縮檔案 |