The Christian liturgy takes up the usage of the Old Testament, in which kings, priests and prophets were anointed with the oil of consecration, as they prefigured Christ, whose name means "the Lord’s Anointed".
Roman Missal. Maundy Thursday
Vessels containing the oils that the bishop blesses and consecrates during the Chrism Mass.
Virgin olive oil is used to prepare the oils, to which essence of nard is added.
Learn more on Chrism Mass Ceremony at this source: http://textosparalaliturgia.blogspot.com/2017/04/misal-romano-tercera-edicion-jueves.html