Soul Stealer

Soul Stealer is an enchantment from Soul Shards that, in pre-1.5 versions, can only be applied to the Vile Sword, post-1.5 versions allow the enchantment to be added to any weapon or book. It increases the number of souls obtained from killing mobs. Only 4 levels can be obtained on an Enchantment Table; level 5 can be obtained by combining two level 4 swords or books on an Anvil.

You can also obtain this enchantment on a Book.

Level of Soul Stealer Souls trapped per kill
0 (Native Vile Sword) 1
1 2
2 3
3 4
4 5
5 6