I have just released an update to libess. What is libess? Its a C++ library that reads an ess file and stores all the information in a bunch of classes so you can do stuff with that information.

The download is here

http://www.cncmods.net/files/libess.zip

Its purpose is to provide a way to read, parse and save the oblivion ess, esm and esp files in exactly the same way the game code does. Its purpose is also to provide a better reference for the format of the ess, esm and esp files than the Wyre Bash source, CBash source, tes4edit source and wiki. (all 4 of which I have used as references for this work, along with exhaustive reverse engineering of the game and construction set code)

New in version 2.0 is support for reading/saving esp and esm files. It can either be used to open an individual esp/esm file or if you open an ess file, it will look into the registry, find your oblivion folder and read the relavent esp/esm files that the save file references.

Things it doesn't currently decode:

1.REFR, ACRE and ACHR change records

2.Compressed form records.

and 3.GMST, GLOB, CLAS, FACT, HAIR, EYES, RACE, SOUN, SKIL MGEF, SCPT, LTEX, ENCH, SPEL, BSGN, ACTI, APPA, ARMO, CLOT, CONT, DOOR, INGR, LIGH, STAT, GRAS, TREE, FLOR, FURN, WEAP, AMMO, NPC_, CREA, LVLC, SLGM, ALCH, SBSP SGST LVLI, WTHR, CLMT, REGN, QUST, IDLE, PACK, CSTY, LSCR, LVSP, ANIO, WATR, EFSH, PGRD, WRLD, ROAD, LAND, DIAL and INFO form records.

Decoding the missing pieces is on my todo list, likely starting with compressed form records.

I will note that it DOES support all of the GRUP records and types (getting that right was HARD) as well as CELL/REFR/ACHR/ACRE form records (also hard to get right)

I believe that libess provides (or will once the missing pieces are implemented) the most comprehensive set of code for manipulating oblivion ess, esp and esm files out there (more comprehensive even than cbash)