oil of oregano is an essential oil and you would have to distill it to get EXACTLY oil of oregano, but you could probably make a tincture... it wouldn't be as strong, but you would still get the benefits.

It's difficult to extract essential oils without expensive distilling equipment, and you'd need a LOT of plant to make it worthwhile. However, try this just for fun:

Cram a saucepan tightly with oregano leaves, and cover with water. With lid ON, bring to the boil, and then simmer for a while. Once or twice, squash the leaves with a wooden spoon to help release the oil. If you're very lucky, you might see some oil floating on the top of the water. It will evaporate quickly.Syphon it off as best you can, and bottle it. You might end up with a teaspoonful or so. Remember it won't be pure, because it will have some water in it, so it won't keep as long as distilled essential oil.

A tea from the leaves is used to aid digestion, to relieve flatulence, to increase sweating and to encourage menstruation. It may be taken to treat respiratory conditions such as coughs, tonsillitis, bronchitis and asthma. As a steam inhalant, it clears the sinuses and helps relieve laryngitis.

The oil is a powerful antiseptic/bactericide/antifungal. It's best to dilute it for all uses. The tea has similar benefits, but not so strong. You can use it for wiping over kitchen and bathroom surfaces, or as a foot-bath for tinea.

Folklore: The leaves are used to gain a favorable outcome in lawsuits. They are also used to keep you in-laws away.(!)