Drop a .ess save here, or browse
C:\Program Files (x86)\Steam\steamapps\common\Oblivion\Saves
Mods that move, add, or remove collectibles will throw the results off.
Find the Potions of Encumbrance you are missing
Each Potion of Encumbrance permanently raises Encumbrance by 10, and there are 27 of them. The wikis list fewer, because several exist only inside a quest.
That is what makes them the easiest set to lose. A good few are gone for good once the quest holding them ends, so it is worth knowing which ones you are still owed before you finish a questline.
What this page does
Drop your save in above and it works out which of the 27 Potions of Encumbrance you have already taken. Whatever is left is listed with the location of each one and pinned on the world map, so you can see which corners of Nehrim still owe you something and clear them in one trip instead of one at a time.
The save is read in your browser. Nothing is uploaded, and there is nothing to install.
If you would rather see everything at once, the full tracker covers all five kinds of collectible together.
