I am a doTERRA Wellness Advocate:
The FDA does not regulate Essential Oils, but they have to contain 20% pure oil. Most oils will have some therapeutic benefit to them however, most contain fillers such as jojoba oil, almond oil, etc which can go rancid over time. What you want to know of that 20% is how pure is it and where does it come from.

doTERRA sources their oils from over 26 different countries, where the plant grows indigenously so the soil is pure and the climate is right for that plant.
doTERRA takes care in ensuring that the plants are harvested at just the right time so that the chemical constituents are of the highest quality to give you the most therapeutic benefit.

Their oils are steam distilled or cold pressed and the process is carefully performed which adds to the quality of the chemical constituents you receive as the final result.

Yes, they do third party testing for chemicals, toxins, pathogens (because they are organic) and if a batch does not meet all of doTERRA’s requirements for safe use as well as therapeutic benefit, it is discarded.
doTERRA is the ONLY CPTG (certified pure therapeutic grade) essential oil on the market today. You can use their product aromatically, topically and internally.