Oblivion Tweaks

Edit your Oblivion .ini file to put these tweaks into effect.

uGridDistantTreeRange=15
Raise to increase area in which LOD tree billboards are drawn - looks quite nice doubled if your PC can take it.

uGridDistantCount=25
Raise to increase the number of LOD tree billboards drawn - looks quite nice doubled if your compute can take it.

uGridsToLoad=5
Raise to increase the X/Y dimension of the number of high detail exterior cells loaded - should be an odd number, 3 or greater. This is quite a performance hit with anything above 5. If there are 25 cells loaded at a time with a value of 5, then there are 49 cells loaded with a value of 7 and so on. I would not recommend going above 7 or 9, but terrain looks nicer if your computer can take it.

uNumDepthGrids = 3
Raising the above tweak can cause the reflections in the water to get messed up sometimes, changing this value to 1 can alleviate that.

bUseWaterReflectionsMisc=0
bUseWaterReflectionsStatics=0
bUseWaterReflectionsTrees=0
bUseWaterReflectionsActors=0
Set these to 1 to allow said objects to reflect in water.

fDlgFocus=2.1000
Raise to pull camera back some in dialogue.

bForceFullLOD=0
A value of 1 forces foreground trees to always render at the highest detail - I haven't found this to be a huge performance hit for the visual benefit, your mileage may very.

iMaxGrassTypesPerTexure=2
Raise to allow more unique grass types per terrain texture - 4 should be enough to let you see everything possible.

iMinGrassSize=80
Raising causes grass to be less dense, change it to a fairly high number. Range between 120-300. The higher the number the less dense the grass is. I changed mine to 200. This makes the grass very thin and sparse.

fGrassEndDistance=4000.0000
Tells the game how far away to draw the grass to, 15000 is quite a long distance.

fGrassStartFadeDistance=3000.0000
How far away the grass will start to fade in, only works if HDR is enabled...

bDoSpecularPass=1
Setting to 0 turns off Specular lighting, but can cause a crash when going into the Wynon Priory, in the beginning of the main quest.

bDoDiffusePass=1
Setting to 0 turns off Diffuse lighting, which makes everything nice and dark...pitch-black dark...but, on the FX series of cards, raises your FPS by about 30.

bDoAmbientPass=1
Setting to 0 is more of a fix for the one above, I have found...it makes everything fullbright, but I believe you can only set it to 0 if the one above is also set to 0...note that having this and the one above turned off, and specular on, can also cause a crash in Wynon Priory in the main quest.

The last three are mainly fixes for those with FX video cards - they can apparently yield a 30 FPS boost but can have very strange effects on lighting (dark caves are fully lit, night and day appear identical).

Source: elderscrolls.blogspot.com