I freeze chopped fresh rosemary in ice cube trays in oil, usually a light oil like olive oil. Basically you chop up your herbs, put them in the tray, and then pour whatever your preferred cooking oil is over them then freeze them. I've heard that some people use butter as well but it should be unsalted so it freezes properly. It really depends what dishes you are planning on cooking and whether they call for oil or butter, and what kind of oil. I've never tried this with oregano, but I'm sure it would work for that too. I would just avoid doing it with stuff like basil, parsley, etc which you wouldn't be cooking anyway.