An essential oil is a liquid that is generally distilled (most frequently by steam or water) from the leaves, stems, flowers, bark, roots, or other elements of a plant. Essential oils, contrary to the use of the word oil are not really oily-feeling at all.Most essential oils are clear, but some oils such as patchouli, orange and lemongrass are amber or yellow in color. Essential oils contain the true essence of the plant it was derived from.Essential oils are highly concentrated and a little goes a long way. Essential oils are not the same as perfume or fragrance oils.ost essential oils are clear, but some oils such as patchouli, orange and lemongrass are amber or yellow in color. Essential oils contain the true essence of the plant it was derived from.