What is the BSA file format?
Files with the .bsa extension are associated with games published by Bethesda Softworks. The format was introduced in 2002 with *The Elder Scrolls III: Morrowind* and has been used across the Elder Scrolls and Fallout series through *The Elder Scrolls V: Skyrim Special Edition*.
What kind of data can .bsa files store?
.bsa files store game assets and resources required for the game to run, including:
- graphics and 2D/3D textures (such as .DDS files),
- audio tracks and samples,
- 3D models and meshes (such as .NIF files),
- characters, inventory items, and world objects,
- dialog text,
- scripts and AI behaviour data.
.bsa is a proprietary binary archive format for storing game resources developed by Bethesda Game Studios. Archives begin with the ASCII tag BSA\0 followed by a version number - 103 for Oblivion and Fallout 3/New Vegas, 104 for Skyrim Legendary Edition, and 105 for Skyrim Special Edition, which introduced LZ4 compression alongside the existing zlib option. Starting with *Fallout 4* (2015), Bethesda replaced .bsa with the newer .BA2 format for all subsequent titles.
Can .bsa files be opened manually?
The .bsa format is a binary archive and cannot be edited with a plain text editor such as Notepad. Dedicated tools exist that allow users to browse, extract, and repack .bsa archives - the most common being BSA Browser (by AlexxEG) and Bethesda Archive Extractor. Users can modify the contents of .bsa files to change gameplay or game-world elements and settings. Such modified archives are distributed as official or unofficial mods, which can be downloaded and applied to the target game.
Security & safety
RISK: MEDIUMA BSA is asset data, not an executable, so the archive itself doesn't run code - but it can contain compiled Papyrus scripts and is distributed as part of mods, which are community-made. Download mods only from reputable sources (Nexus Mods, Bethesda.net), and beware archives bundled with unexpected .exe files. Extract with a trusted tool (BSA Browser, BAE) rather than running anything from an untrusted pack.
Format details
in a nutshellPrograms that open BSA files
Windows5 apps
Dragon UnPACKer
Free General game-archive explorer that can open older BSA archives to browse/extract. 
BSA Browser (AlexxEG)
Free Open the .bsa to browse its tree; select files to preview, and extract single files or the whole archive.
Bethesda Archive Extractor (BAE)
Free Open a .bsa (and .ba2), select assets, and extract them to loose files - handles all BSA versions and BA2.
Archive2 (Fallout 4 Creation Kit tool)
Free Bethesda's official packer/unpacker (ships with the Fallout 4 Creation Kit) - extract or repack archives.
The Elder Scrolls / Fallout (the game)
Paid The game loads the .bsa at launch when a matching plugin/INI entry is active; the archive is not opened standalone. Technical details
deep spec| Format type | Proprietary binary game asset archive |
| Magic bytes | "BSA\0" (0x42 53 41 00) at offset 0 for Oblivion/Skyrim-era archives; Morrowind BSA starts with version value 0x00000100 and has no ASCII tag |
| Byte order | Little-endian |
| Format versions | v100 (Morrowind), v103 (Oblivion, Fallout 3, Fallout: New Vegas), v104 (Skyrim Legendary Edition), v105 (Skyrim Special Edition) |
| Compression | Optional per-file zlib (v103/v104) or LZ4 (v105 Skyrim SE); individual files may also be stored uncompressed within the same archive |
| Encryption | None; no digital signature or whole-archive checksum |
| Internal structure | Header, folder-record and file-record tables indexed by FNV name hashes, a name string table, then concatenated optionally-compressed data blocks |
| Filename lookup | FNV/CRC hash-based indexing of folder and file paths; hashes are used for lookup only, not for integrity verification |
| Typical archive size | Tens of MB to several GB; full game asset archives routinely exceed 1 GB |
| Content types stored | Meshes (.nif), textures (.dds), audio, voice, scripts, animations, shaders, and other loose game assets |
| Plugin loading behaviour | Game auto-loads a .bsa when a plugin (.esm or .esp) sharing the same base filename is active, or when the archive is listed in the game INI file |
| Platform support | Windows (PC), Xbox, PlayStation |
| Successor format | BA2 ("BTDX" magic tag) introduced with Fallout 4 (2015) and used for Fallout 76 and Starfield; .bsa is not used in those titles |
| Modding tooling | Archives can be inspected and repacked with BSA Browser (AlexxEG), Bethesda Archive Extractor, Dragon UnPACKer, and Archive2 from the official Creation Kit |
| Released | 2002 (The Elder Scrolls III: Morrowind) |
| Latest version | BSA v105 (Skyrim Special Edition, 2016); succeeded by BA2 for Fallout 4 / Fallout 76 / Starfield |
| Specification | en.uesp.net |
BSA conversions
Community Q&A
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