At the Chrism Mass, which is usually celebrated on Holy Thursday, the bishop consecrates three oils — the Oil of Catechumens (“Oleum Catechumenorum” or “Oleum Sanctorum”), the Oil of the Infirm (“Oleum Infirmorum”), and Holy Chrism (“Sacrum Chrisma”) — which will be used in the administration of the sacraments throughout the diocese for the year.

The Oil of Catechumens is used in the preparation of the catechumens for their baptism. The Oil of the Infirm is used to bring comfort and support to the sick. The Holy Chrism consecrated by the bishop is used to anoint the newly baptized, to seal the candidates for confirmation, and to anoint the hands of priests and the heads of bishops at their ordination, as well as in the rites of anointing pertaining to the dedication of churches and altars.
-Ceremonial of Bishops, 274-