An oscillating propeller type aerator apparatus for more efficiently aerating a liquid is disclosed. The oscillating propeller type aerator apparatus for aerating a substance according to the present invention includes a propeller type aerator and an oscillating support system. The aerator includes a tube, a propeller, and means for rotating the propeller. The oscillating support system supports the aerator with the tube and propeller at an acute angle below the surface of the substance to be aerated. The support system includes a mechanism for oscillating the tube and propeller through an angle about an axis transverse to the surface of the substance to be aerated in order to disperse over an arc related to said oscillating angle, air injected through said tube into the substance.