We consider a generalization of the maximum ow problem in which the amounts of ow entering and leaving an arc are linearly related. More precisely, if x(e) units of ow enter an arc e, x(e) (e) units arrive at the other end. For instance, nodes of the graph can correspond to di erent currencies, with the multipliers being the exchange rates. We require conservation of ow at every node except a given source node. The goal is to maximize the amount of ow excess at the source. This problem is a special case of linear programming, and therefore can be solved in polynomial time. In this paper we present the rst polynomial time combinatorial algorithms for this problem. The algorithms are simple and intuitive.