It is demonstrated that the total flow in the optimum cascade composed of three different types of gas centrifuges with varied separative performance levels and overall separation factors varying over the cascade stages is less than that in the corresponding ideal (non-mixing) cascade. The data obtained make it possible to use the parameters of the optimum cascade to find the operational mode for the cascade stages that provides the minimum total flow in a separation cascade. (C) 2014 Elsevier Ltd. All rights reserved.