I got my females at the local Petsmart but had to travel to another city to get males becuase Petsmart here only gets females. They were more expensive at 14 bucks each from Petsmart but thought it was a good invest ment! I have had 60 babies from 6 moms al within a week. Any rats that are of the oposite sex should do just fine. Though I do have a few that seem to not get prego and a male that seems to can't get any prego. So it all depends on what you get. There really is no way to tell so it is all luck I guess. Good Luck!