A simple and effective method is presented for the sizing and passage apportionment of multistream plate-fin heat exchangers. Methods for passage arrangement are discussed and it is shown that a symmetric or ＇＇mixed＇＇ passage arrangement is more efficient than a ＇＇segregated＇＇ arrangement. A method for assessing the relative merits of various passage arrangements is presented. The use of the methods is illustrated through a worked example.