A high efficiency mixing device for mixing first and second fluids within a conduit. A biscuit element is positioned at the upstream end of the conduit having a longitudinal axis that coincides with the longitudinal axis of the conduit. The biscuit element is provided with a plurality of openings including a central opening positioned along the longitudinal axis and a plurality of additional openings spaced proximate to the central opening. The openings are provided with primary mixing elements which induce a rotational angular velocity to a first fluid passing therethrough of the same rotational sign. Second fluid feed ports are positioned within each of the openings for introducing a second fluid to the first fluid as the first fluid passes through the openings and into the conduit. Secondary and tertiary mixing elements are optionally located downstream of the biscuit element to enhance the mixing of the first and second fluids.