Holy Oil
From Super-wiki
Castiel obtains some Holy oil from Jerusalem. It can be used to trap an angel by having them inside a circle of it and igniting it. Meg was burned by the fire that trapped Castiel; but despite clearly being hurt by it she probably survived.
Contents
Uses of Holy Oil
5.03 Free To Be You And Me
Raphael is trapped by Castiel and Dean this way in . They leave him in the still burning circle.
5.08 Changing Channels
Sam and Dean use it to trap Gabriel, but later release him.
5.10 Abandon All Hope
Lucifer uses it to trap Castiel, but he manages to break the circle and escape.