USDA scientists, whose findings appeared in the Journal of Agricultural and Food Chemistry, report that herbs have higher antioxidant activity than fruits, vegetables and some spices, including garlic.  See here for the journal article.

Oregano in particular stood out for its beneficial properties:  “The herbs with the highest antioxidant activity belonged to the oregano family. In general, oregano had 3 to 20 times higher antioxidant activity than the other herbs studied.”

Turkcu et al, in a study published in the International Journal of Clinical and Experimental Medicine, found that carvacrol, a compound found in oregano oil, reduced intestinal toxicity in a certain cancer treatment drug.