Hi, http://www.p-73.com This is the website of the North American Herb & Spice company. Maybe you can learn it from there.. You can buy this brand's oil from your local health food store.
All I know is that it takes a LOT of wild oregano to extract oil. And it is not an easy process as I had read somewhere... By the way, Wild oregano is available only in Turkey and Greece. And only Turkey prepares its oil for commercial purposes. It is very very cheap in Turkey, just $7/bottle versus ~$50/bottle in US. My suggestion would be to order some from a Turkish grocery in US, (I guess they may sell it higher than in Turkey though...)
Even Barefoot Herbalist on a forum in Curezone does not produce his oil of oregano, and imports from Turkey to sell in US.
I have brought 7 bottles from Turkey for my own use, since I know how insanely expensive it is here in US.