If the coffee beans appear very oily, then to me the most likely roasted with margarine (NOT BUTTER)!
Old liao, better avoid these kind of margarine-roasted coffee, else easy get heart-attack and stroke... Old people better avoid!
From what I see and searched before, only Robert Timms brand has pure 100% coffee bags, the rest of the brands are all margarine roasted!
End up if I need to go overseas to places where I may not get machine-made coffee (not 3-in-1 type), I just grind the 100% pure coffee beans at home and put in those food-safe tea/coffee filter bags to bring overseas.