All of this has led over the last 50 years to an expanding industry in synthetically produced "essential oils." These advancements in the field of chemistry have flooded the market with these low-cost imitation fragrances, which are today the basis of almost all perfumes, cosmetics and a rapidly growing number of synthetics passed off as "essential oils".
If the oil you're purchasing seems inexpensive for a rare or quality oil (less than $50 for frankincense) think twice about your purchase.
There are few companies who can boast what would be considered "biblical grade," "medical grade" oils, or certified pure, free of contaminates and synthetics which would have been the standard in ancient times. dōTERRA essential oils are certified pure therapeutic grade, and are undeniably among the purest most potent oils available on the planet. They are harvested in their indigenous environment producing the chemical constituency that can only be found at their original source

The Holy Spirit is often depicted as oil. One reference is in the Parable of the Ten Virgins found in Matthew 25.

Because of its abundance of well-known symbols, the Parable of the Ten Virgins is perhaps the easiest to understand in a prophetic light. The Bridegroom, of course, is Christ. Virgins are often symbols of individual Christians. Lamps are vessels that contain oil, a common symbol of God's Spirit, thus they represent salvation through Jesus. The wedding refers to the marriage of the Lamb to the church (Revelation 19:7). In these verses Jesus seems to be referring to the presence of the Holy Spirit. These virgins were waiting for the Bridegroom, which pictures Christ’s coming for His bride the church (also known as the rapture of the church) to which He is presently betrothed (or engaged) to. 
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​Five were ready when the Bridegroom arrived and already had the oil in their lamps. But the other five, the foolish ones, were not prepared. They had to run out and buy some oil, but they were too late. They had procrastinated and failed to betroth themselves to Christ. When they came back, they said, “'‘Lord, lord, open to us.’ But he answered, ‘Truly, I say to you, I do not know you.’ Watch therefore, for you know neither the day nor the hour” (Matt 25:11b-13). Those who knew Christ, by having the Holy Spirit (oil) were prepared for His coming.