You can get Soul Gems in Oblivion from several sources:

• Looting and Farming : Enemies like necromancers often carry Soul Gems, so killing and looting them is effective. Cave farming, especially killing necromancers, is a good way to gather many Soul Gems

. Also, some chests in dungeons contain Soul Gems that respawn after waiting in-game time, such as the chests found in the Ceyatatar dungeon accessed via a trap door, which can be farmed repeatedly by waiting 73 hours in total for respawn

• Buying from Vendors : Mage Guild shops and general goods merchants in major cities sell Soul Gems, including Petty, Lesser, Common, Greater, and sometimes Grand Soul Gems. Their stock refreshes every 7 in-game days but is limited and can be expensive

• Quest Rewards and Guild Progression : Joining and progressing through the Mage Guild questline, especially becoming Arch-Mage, grants access to many Soul Gems found in the guild halls and as quest rewards

• Special Soul Gems :
  • Azura's Star , a reusable Grand Soul Gem, is obtained by completing Azura's Daedric quest at the Shrine of Azura north of Cheydinhal

* _Black Soul Gems_ , which can trap humanoid souls, are created by placing a Grand Soul Gem on specific necromancer altars during the Shade of the Revenant event, such as at Dark Fissure or Wendelbek ruins, and using the Soul Trap spell

• Finding in the World : Soul Gems can also be found scattered in chests, sacks, crates, and display cases throughout the game world, especially in magical locations like the Arcane University or dungeons

In summary, the best methods to get Soul Gems are farming necromancers and specific dungeons, buying from mage vendors, completing Mage Guild quests, and obtaining special gems through quests or necromancer altars