So I've been smoking for a while and have smoked oil a few times. I am interested in buying a g pen but I have no idea what to expect from buying one. Do I just buy oil, put it in the chamber and use it or is a lot more difficult than that? And how much oil do you need and how many hits does that oil usually give you for the pen? I know oil is a lot more expensive than bud but I'm not really sure how much?