You can get Grand Soul Gems in Oblivion (and Oblivion Remastered) reliably from a mix of static world locations and repeatable merchant sources.

Main ways to get Grand Soul Gems

1. Guaranteed world spawns (static locations)

These are fixed Grand Soul Gems placed in the world, usually behind Very hard locks or in remote dungeons.

  • Arcane University (Imperial City)
    • Arch‑Mage’s Lobby: 3 in display cases behind a very hard lock.
* Mages’ Quarters: 1 more in a locked display case, sometimes another on a desk in the enchanting building.
  • Chorrol Mages Guild
    • Main floor: 2 Grand Soul Gems in one display case (very hard lock).
* Another display case to the left of the front door holds 3 more.
  • Drakelowe
    • In the basement, reached via the hidden fireplace/trapdoor in the house. Contains 1 Grand Soul Gem.
  • Crayfish Cave
    • Along the Corbolo River to the south/southeast; 1 Grand Soul Gem inside.
  • Nornal (Ayleid ruin)
    • West of Drakelowe, near the “N” in “The Nibenay Basin” on the world map; 1 gem found among the ruins, often near or behind a lich.
  • Squandered Mine
    • Northeast of Drakelowe; 1 gem behind a secret door on the lowest level, guarded by undead.
  • Swampy Cave
    • In the Dry Rock Run section, in a chest in the large room with two swamp trolls (platform‑dependent availability).

These are excellent targets if you need a small batch quickly (like for crafting or quests) and don’t mind breaking into places.

2. Buying Grand Soul Gems (repeatable sources)

Once you’ve looted the guaranteed ones, merchants are your main renewable supply. Their stock refreshes every few in‑game days.

  • Mystic Emporium – Imperial City Market District
    • Merchants Aurelinwae and Calindil can sell Grand Soul Gems (sometimes empty, sometimes filled).
  • Other Mages Guild halls
    • Many guild hall merchants have at least 1 Grand Soul Gem for sale, and their inventories reset over time.
* You can also pickpocket these from the merchants if you’re playing a stealth build.

If you need a lot, a simple loop is:

  1. Fast travel between guild halls and the Mystic Emporium.
  2. Buy any Grand Soul Gems you see.
  3. Wait 3–7 in‑game days to reset inventories.

3. Quest and dungeon “possible” spawns

Some locations can have Grand Soul Gems but are not guaranteed every time; they roll on leveled lists.

  • Ayleid ruins
    • Ayleid casks and other containers (e.g., Anga and similar ruins) can spawn Grand Soul Gems, especially at higher levels.
  • Mythic Dawn / Dagon Shrine
    • A chest in the Dagon Shrine living quarters can spawn a Grand Soul Gem while you’re infiltrating the Mythic Dawn.
  • “Sins of the Father” quest
    • This quest can yield multiple filled Grand Soul Gems, though they are not empty and are more for soul‑powered use than for special empty‑gem requirements.

4. Special case: empty Grand Soul Gems for Vampire Cure

If you’re doing the “Vampire Cure” quest, you need 5 empty Grand Soul Gems, which can feel rare.

  • Progressing the cure quest unlocks:
    • Extra access to Drakelowe , Squandered Mine , and Crayfish Cave , each with empty Grand Soul Gems you can loot.
  • You can also:
    • Buy empty Grand Soul Gems from the Mystic Emporium (Calindil and Aurelinwae – check that the gem is empty, not filled).
* Steal or pickpocket empty gems from Mages Guild halls and Arcane University display cases, if you don’t mind going criminal.

Some players also use the classic item duplication glitch on an empty Grand Soul Gem once they’ve found one, if they’re not concerned about “cheesing” the game.

Quick reference table (static & easy sources)

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Location / NPC How to get Grand Soul Gems Notes
Arcane University Steal from display cases in Arch‑Mage’s Lobby & Mages’ Quarters (very hard locks). Several guaranteed gems; some may be pre‑filled on certain platforms.
Chorrol Mages Guild Steal from two main‑floor display cases. Total of up to 5 Grand Soul Gems behind very hard locks.
Drakelowe Loot gem in basement via hidden fireplace entrance. Useful during Vampire Cure line.
Crayfish Cave Loot gem inside the cave along the Corbolo River. Quest‑related for Vampire Cure, good for empty gems.
Squandered Mine Loot gem behind secret door on lowest level. Guarded by undead; another Vampire Cure target.
Mystic Emporium (Calindil & Aurelinwae) Buy Grand Soul Gems from both shopkeepers. Stock can include empty and filled gems; refresh by waiting.
Mages Guild merchants Buy or pickpocket Grand Soul Gems. Most halls carry at least one; inventory resets over time.
Ayleid ruins & Dagon Shrine Search chests and Ayleid casks. Random/leveled spawns; not guaranteed every run.
**TL;DR:** Hit Arcane University and Chorrol Mages Guild for guaranteed early Grand Soul Gems, then farm the Mystic Emporium and Mages Guild merchants with inventory resets for an ongoing supply, and use Drakelowe/Squandered Mine/Crayfish Cave plus merchants if you specifically need multiple empty Grand Soul Gems for the Vampire Cure.

Information gathered from public forums or data available on the internet and portrayed here.