Abstract: Compounding apparatus and methods are provided for accurately compounding multiple source solutions in an efficient and automated manner. Liquids are transferred from their respective source solution containers to a common mixing chamber by pumps which are disposed between the source solution containers and the mixing chamber and fluidly connected to respective source solutions, and a controller which controls the pumps to operate in either fluid pumping mode or air pumping mode based at least in part on signals received from weight indicating devices associated with the tubing which extends between the pumps and the mixing chamber and/or weight indicating devices associated with the mixing chamber.