Multipath routing is expected to improve the degree of control in network flow managements. Therefore, multicriteria designs will become indispensable for the next generation of multipath routing algorithms and protocols. This paper shows a theoretical approach to multipath routing problems as a multi-objective optimization of network flows. Two objectives, total link utilization and bandwidth fairness for connections, are introduced into an objective formulation which is solved with a nonlinear programming solver. The numerical analysis shows that drastic fairness improvement can be achieved with small decline of utilization. Compared to standard multipath routing, this approach of bandwidth fair multipath routing can achieve a variance of bit-rate for all connections of 0.0123% with a decline of utilization of 11.4%. In case of single path, a variance of 0.0168% with decline of utilization of 39.7% can be achieved. Finally, the controllability of multipath routing is discussed.