Oblivion modding occurs almost entirely in the game’s Data folder. When you first install the game, about the only thing in there is a batch of BSA archives containing its standard assets: textures, meshes, fonts, music, etc. These are never touched by the mods you install. Instead, the game looks for any replacement files subsequently dropped into the Data folder. So, if you drop in a mod containing replacement textures for the game’s races, it’ll use those instead while leaving the vanilla files intact.

This makes it very easy to try out different mods without critically endangering the game. In the event that one proves unstable or unsuitable, you can just delete the files and things revert to normal. Alternatively, as you’ll read about shortly, you can often disable the mod’s plugin file without removing it entirely.

Things get complicated, though, as your list of mods grows. In all likelihood, you’ll want to remove one mod while leaving the rest of them intact, which given the drag-and-drop nature of the above process can be difficult. All those files dropped into a single folder, often overwriting each other, become a haystack to the needles of individual mods.

With that in mind, let’s have a look at what a modded Data folder might contain:

1. The Textures and Meshes folders are the two you’ll work with most, often both at once. A completely new piece of armour, for instance, will need a new 3D mesh and a new texture to put on it. A high-res texture pack will, by its nature, only use the Textures folder. Any custom entity like hair or a body replacer will again use both.
2. Created by Bethesda’s free Elder Scrolls Construction Set, ESP plugin files change the game’s entities, events and behaviour. In other words, rather than just change how it looks (like a texture or mesh replacement) they change how it behaves. So, that aforementioned new piece of armour will need an in-game object id and, ideally, a place where you can buy or discover it. An ESP file takes care of both. Quests, dialogue, weather, special effects, properties, spells: you name it, an ESP can change it. Oblivion finds and implements these at runtime, and you can easily toggle them on and off using its own launcher or, preferably, Oblivion Mod Manager, which is described later.
3. This DistantLOD folder was created by a tool you’ll read about shortly, TES4LODGen.
4. OBSE, the Oblivion Script Extender, is described in the Essential Tools section. Plugins for it can be dropped into this folder and will be run automatically.
5. The Shaders folder contains shaders used by the Oblivion Graphics Extender mod. These can include Screen Space Ambient Occlusion (SSAO), colour filters, depth of field and god rays. I don’t actually use  these any more because they disable anti-aliasing and I’m not entirely sold on the effects themselves. Still worth a look, though.
6. Bash Patches are used by the hardcore modder’s tool of choice, Wrye Bash. It’s covered briefly in the Essential Tools section but you should really investigate it yourself. Let’s just say it’s complicated.
7. Oblivion uses BSA archives to store its vanilla assets. Some mods, rather than scatter their files across numerous subfolders, prefer to use the same format for a cleaner install.

Mod Compatibility and Load Order

Hardware limits aside, the most common problem you’ll encounter when modding Oblivion is compatibility between the mods. Many of the mods featured here are massive, sprawling things which add or change hundreds of files. Few have been made with other mods in mind, so conflicts between them are inevitable. That said, no author wants his mod to have a negative press, so most will advise you of any known conflicts in their readme files – so read them. ESP files, meanwhile, don’t make changes as obvious as copying and overwriting files, but still change values within the game that might tread on another mod’s toes. Again, readme files will usually point out any glaring conflicts, while tools such as OBMM and BOSS (featured on the next page) help clean up the mess. Don’t expect everything to slot neatly into place right away, but persevere: the right combination of mods can yield stunning results.

Patching The Game: Official vs. Unofficial

If you’re using the Steam version of Oblivion, you won’t have to worry about downloading the latest 1.2.0416 patch – Steam keeps all its games up-to-date. Anyone else, though, should make sure they’re running this latest version. Some of the more expansive mods require it, as does the thing you should arguably install before any modding, the Unofficial Oblivion Patch. This doesn’t tamper with the game’s rules or interfere with other mods – quite the opposite, in fact – so there’s no reason not to use it. Here’s the author’s description:

“This mod is a joint effort to fix the vast amount of bugs currently existing in Oblivion v1.2.0.416, fixing over 1,800 bugs so far! If you’re experiencing a bug with Oblivion and it’s not fixed by our mod please by all means report the bug to us in as much detail as possible so we can try to fix it! Also if you find any: levitating trees or rocks, see-through or fall-through walls/objects or other stuff out of place, please let either of us know. To get the exact location, use the console commands sdt 0 and then tdt, click the item, note the Cell (not PC Cell) and form ID value (the eight hexadecimal digits at the top, ie 00123ABC) and indicate what’s out of place. You can use tdt again to toggle the debug display off. Thank you and we hope you have a better Oblivion experience!”

Oblivion and Steam

The only ‘problem’ I’m aware of with modding a Steam version of Oblivion is that the Oblivion Script Extender – a very useful plugin – has a slightly different install process. Because Oblivion keeps its core files secure from any modding efforts, letting modded files supersede its own at runtime, there is no issue with file integrity. Modding with Steam is barely any different, therefore, to a regular installation.

No-CD patches

People always advise caution when using ‘No-CD’ patches, but I suspect that’s more of an ethical issue. Obviously, you have to be careful when executing any thirdparty binaries, and I’m taking it for granted that you have an up-to-date virus scanner. But the benefits of skipping the game’s disc check are equally obvious, and so long as you haven’t pirated the game, your conscience should be clean. This isn’t an issue for the Steam version. I always install from the same disc version of the game I bought at launch, and yes, I do use No-CD patches which I get from here. Not once have I had a stability or performance issue I could blame on them.

Save Your Saving

You know those tooltips that say, ‘Regularly save your progress.’ Don’t – at least until you’ve got your biggest mods set up. The thing with Oblivion – and again with Fallout 3 – is that there’s more to a save than just who and where you are. The countless variables that make the world of Cyrodiil tick are stored in there, and they don’t always take kindly to having that world changed around them. If you keep changing mods, trying them out, saving, quitting and repeating, what you tend to get is a slow but undeniable drop in stability and performance. Some mods might not even work at all. If you can stomach it, the best bet is to just get your mods in order and then start a new game entirely.