When hair is left feeling greasy, heavy, or oily after the shampoo process, it is often the result of any of the following: a) too much oil was used in the pre-shampoo, b) the choice of oil was too heavy for the hair profile or c) the oil used was sealing as opposed to penetrating. The key to pre-shampooing is to use a penetrating oil that suits your hair profile and using only enough to lightly coat the strands. If your hair is left with residue after washing then it is best to shampoo again as you don't want to leave any oil in the hair.