Kathy- so much will depend on what species of "oregano" you use, how carefully it was grown/harvested, etc...
It certainly isn't going to be the "same" as oil of oregano, which I'm sure is distilled from tons and tons of oregano leaves, like all essential oils.
But I've used plain kitchen oregano as part of a strong anti-infection soak when I didn't have oregano essential oil, and I believe it had value in that form.
You'd almost certainly have to use a LOT more tincture or strong decoction than you use of the oil, but I'd try it if I didn't have the oil.
I grow the very powerful "Greek oregano" (subspecies hirtum) in my herb garden. The difference in that plant and common oregano is stunning.. it's spicy, even peppery even when you nibble a fresh leaf. This is what I use now for oregano infusion or decoction for sore throats or soaking small infections.
The great thing about essential oils as a prep item is their very long shelf life, if they're stored properly. Money can be a problem in laying up a large supply, but if you can afford it, you can certainly keep them for 5 years, if you keep them cool, dry and dark.
Summerthyme