Exorcism
In Catholic Christianity, exorcisms are performed in the name of Jesus Christ. A distinction is made between a formal exorcism, which can only be conducted by a priest during a baptism or with the permission of a bishop, and "prayers of deliverance" which can be said by anyone.
The Catholic rite for a formal exorcism, called a "Major Exorcism", is given in Section 11 of the Rituale Romanum. The Ritual lists guidelines for conducting an exorcism, and for determining when a formal exorcism is required. Priests are instructed to carefully determine that the nature of the affliction is not actually a psychological or physical illness before proceeding.
Gabriele Amorth
In October 2000, it was reported he had performed over 50,000 exorcisms (which ranged from "a few minutes" to "several hours" in length). In March 2010, he said that the number had increased to 70,000 . By May 2013 he said he had performed 160,000 exorcisms in the course of his ministry. Note that according to Father Amorth, each exorcism does not represent a victim of possession, but rather each exorcism is counted as a prayer or ritual alone, and some possession victims required hundreds of exorcisms.