Is it dangerous to ingest aromatherapy oregano oil?

Many of these oils are mixed with petroleum, so don't. If it were pure, then it would not harm you; but it is very likely that it is mixed down to around 4-7% of the actual oil that you want.

(Another answer - former vitamin dept. manager) - Essential oils used in aromatherapy are NOT appropriate for ingestion.

What you're looking for is food-grade (capsule or liquid) oregano oil. The most popular vitamin (internal) one that I carried was called Oreganol (liquid) and OregaMax (capsule), made by North American Herb and Spice. Those are commonly used by folks who are looking for the immune system-supporting effects of oregano oil. Some essential oils in pure form are ok to ingest, but in very small amounts and diluted with alcohol or water, and always under supervision of certified health care practitioner.