The quality of essential oils depends on many factors.
The process by which a substance is obtained,
its state of maturity and its source are all
important.  There are "prize localities" for
certain essences... The yield may vary from
one to ten - which is to say that quality in
essential oils, as in anything else,
has to be paid for.
Valnet, M.D., J., The Practice of Aromatherapy,
Healing Arts Press, 1982, p.27