In tower-type reactors, poor mixing is a major concern in fermentation processes. As an attempt to improve the mixing efficiency, an algorithm based on the analytic solution of the modified network-of-zones model and application of the singular value decomposition technique is proposed to determine the optimal feeding locations and corresponding amounts of feed in airlift reactors, bubble column reactors, and airlift reactors with wire-mesh draft tube. The optimal feeding locations and corresponding amounts of feed predicted by the algorithm are in good agreement with the experimental results. The proposed algorithm is proved to be an effective method for optimizing the feeding operation to improve the mixing efficiency for the three tower-type reactors. (C) 2005 American Institute of Chemical Engineers.