A modification, also known as mod or plug-in, is a software file that changes some aspect of the game or adds new content, such as weapons, armor, or quests. Several official plug-ins exist for the Xbox 360 (see below), but modifications are overwhelmingly most common for the PC platform.
Mods do not come pre-packed with the retail game. They are created by the game's fans, usually using the Elder Scrolls Construction Set for Oblivion. They can be downloaded from the internet, usually for free. Bethesda also offers official studio-built mods, which may be downloaded for a small payment.
Most mods are in the .esp format, and must be enabled as a Data File when the game first loads (see the 'Data Files' dialogue on the PC, as the game loads). Some mods may take the form of textures that replace those in the game, or .xml files that adjust display characteristics. Textures and .xml files do not need to be enabled as Data Files at start-up.
- Horse Armor (DLC1)
- Orrery (DLC2)
- Wizard's Tower (DLC3)
- The Thieves Den (DLC7)
- Mehrunes' Razor (DLC9)
- The Vile Lair (DLC5)
- Spell Tomes (DLC4)
- Knights of the Nine (DLC8)
- Fighter's Stronghold (DLC6)
- However, if you purchased the Game of the Year Edition, it ONLY has the Knights of the Nine and Shivering Isles, but NONE of the others.
For PlayStation 3 users, the Knights of the Nine plug-in is automatically included with the PS3 version of Oblivion. It is not known whether all of the other official plug-ins will be made available for download for that console.