Can I import Morrowind mod files into Oblivion?
Originally the answer was no, because of the large disparities in mod and art file formats. However, tool makers have bridged much of the gap and automatic conversion of most aspects of mods is now possible.
 Overview of Differences
While there is some similarity in the file structure, there are so many differences.
- Art file formats are completely different. You would need to recreate them.
- Oblivion does not offer any models that are directly matchable to Morrowind models.
- Oblivion lacks some things that you expect in Morrowind, e.g., tiling sets for rooms.
- Many of the particulars of the mod file formats are different. Even if you have a translator, a lot of data would need to be filled in by hand.
 Remaining Technical Limitations
- Scripts are not translated. This impacts both regular scripts and dialog scripts.
- Dialog translation is somewhat limited. Morrowind does not use voiced dialog, while Oblivion does. Morrowind dialog is also a lot wordier which does not work as well with the restricted text interface of Oblivion.
- Oblivion, while expanding in many areas, has also shrunk in others. E.g. there are less spell tyes (no levitation, no swift swim). E.g. less skills (no unarmored).
 Legal Limitations
- Bethesda has explicitly forbidden the distribution of translated Morrowind (plus expansion packs) mod and data (Nif files) files. Even the discussion of MorrOblivion -- a tool that automatically converts a user's existing Morrowind esms and data files into an Oblivion equivalent is not allowed on the official forums.
- However, the conversion of fan created esms, esps and art files is okay (assuming appropriate permission from the original author of those works).