Olea Sancta (Holy Oil) St. John the Baptist

The Catholic Culture Dictionary gives this explaination for the Holy Oils:

HOLY OILS
Sacramentals blessed by a bishop. There are three kinds: oil of catechumens, holy chrism, and oil of the sick. The first and third are pure olive oil. chrism has in the oil a mixture of balm or balsam. In 1970, the Congregation for Divine Worship declared that, if necessary, the holy oils may be from any plant and not only from olives. The holy oils are symbols of spiritual nourishment and the light of grace. They are used in the public administration of baptism, confirmation, and anointing of the sick. The blessing of the holy oils normally takes place on Holy Thursday by a bishop at a cathedral church. After distribution locally they are kept in locked boxes in the ambry. Unused oils, a year later, are burned in the sanctuary lamp.