The oil of chrism was actually called "Sacrum Chrism" before the Oil of Chrism. Throughout the whole of the Bible they have all the different uses of oil in all the different sacraments. Oil is important because it can bring us into the Catholic Church this sacrament is called baptism, the Oil of Chrism can also confirm us as Catholics for the rest of our lives this sacrament is called Confirmation.
The Catholic Church started to use Olive Oil and then named it all different names such as Oil of Chrism, the Oil of Infirm e.t.c. So the Oil of Chrism is made of Olive Oil and then later in the Church Year the Priest then blesses the Oil and then names it a special name.