You can use captured souls as material and XP components.
Prerequisites
Any evil alignment, caster level 5th.
Benefit
When casting a spell would require an expensive material component or experience point cost, you can substitute a captured soul in its place. The soul can be captured in any way (soul gems are the most common method), but you must be able to touch the soul or the object in which it is trapped to use it as a material component. The soul itself must be at least equal in value to the gp cost of the material component you are replacing or sufficient consumable experience to cover the experience component (any excess gp value or XP is lost). See Soul Harvesting for determining the value of various souls.
Using a soul in this way frees it from the vessel in which it was trapped. (If this was a soul gem, the gem is destroyed as normal.)
A soul used as a material component is not destroyed, but it suffers significant damage as it is shunted to its final resting place. A creature whose soul has been used as a material component cannot be restored to life via raise dead. Reincarnate, resurrection, true resurrection, and similar high-level effects can restore such a creature to life if the caster succeeds at a DC 20 caster level check. Miracle and wish can restore the creature to life without requiring a check.
Using Soul-Powered Magic is an evil act.