An example of one I would use in water, rather than olive oil, would be mint. I don't think olive oil would do much for mint brownies.
I've also done sage, chives, marjoram, and thyme in water, though olive oil would work for any of those. The water does freeze more solid than the oil. If you are tossing it into stew or tomato sauce or something, the extra liquid really doesn't affect the recipe.