How to Capture a Soul in Oblivion

Purchase a Soul Trap spell or scroll from any Mage's Guild hall across Cyrodiil or from another trader dealing in Soul Trap spells - you cannot capture a soul without one. You will need to have a Mysticism skill of at least 25 to use the most basic Soul Trap spell, although you can be of any level to use Soul Trap scrolls or a weapon with a Soul Trap enchantment on it. The longer the duration of the Soul Trap spell, the better, as you will have a longer time to capture the soul. As an alternative, the sword Umbra (part of the Clavicus Vile Daedric Quest), has a soul trap effect on strike, as do several other magical weapons.

Acquire a soul gem - the types of soul gem are petty, lesser, common, greater, grand and black. Although any soul gem can be used to capture a soul, the larger the soul, the larger the soul gem needed. For example, a mud crab with a soul level of 'petty' can fit in any size of soul gem, but a Minotaur Lord's 'grand' soul level can only be trapped in a grand or black soul gem. Black soul gems are technically like grand soul gems, but can capture NPC souls as well - they can be created using methods discovered during the Necromancer's Moon Mages Guild quest. Soul gems can be bought from most mages stores, in random loot and from Mages Guild halls and range in price depending on their level. In addition, you can obtain Azura's Star, a re-usable Grand soul gem artifact, by completing the Azura daedric quest.

Locate a creature who's soul you want to capture, or if you have a Black soul gem, an NPC (such as an Arena combatant or bandit). The easier the creature is to kill, the smaller its soul level will likely be and the smaller the soul gem you'll need. Creatures such as deer, goblins, mud crabs and rats are easy to practice using Soul Trap spells on. When you become better acquainted with capturing souls, consider tackling larger targets such as Daedroth, Lich and Gloom Wraiths, which have high-leveled souls. If you want to capture an NPC's soul, do so where no one can see you, as casting a soul trap on someone will incur a bounty if spotted.

Cast your Soul Trap spell on the intended target, or hit them with your Soul Trap-enchanted weapon, and kill them with a soul gem in your inventory before the duration of the spell runs out. If you kill them before time runs out, then the creature's soul will fill the most suitable soul gem in your inventory - for example, if you kill a mud crab with its petty soul, it will fill a petty soul gem if you have one. However, if you only have a Grand soul gem, it will fill that with its petty soul. However, if you fail to kill your target before the spell runs out, you will either need to cast the spell again or miss out on the chance of capturing the soul. For this reason, it is advisable to not cast the Soul Trap spell until the target is just about dead, in order to give yourself the maximum amount of time to capture it, or use a long-duration Soul Trap spell.