These fragrance oils are a vegetable base oil with a combination of natural and synthetic materials.
The synthetic materials are highly purified and the essential oils and naturally-derived ingredients are distilled or purified as well. They are sourced from companies that are members of RIFM (Research Institute for Fragrance Materials) and IFRA (International Fragrance Association).
RIFM is responsible for researching candle fragrance materials; IFRA is responsible for interpreting the data from RIFM and setting the codes and standards for fragrance materials. 
They are Phthalate free and most are also suitable for use in soaps, lotions and creams.