Stall stagnation phenomena in the system of axial-flow compressors and ducts are studied on the basis of analytical results by a code on surge transients analysis and simulation with respect to a variety of delivery duct configurations coupled with either a nine-stage compressor or a single stage fan. The stall stagnation boundary was found to be formed mainly by two zones, B- and A-boundaries. The B-boundary tends to occur for plenum-type delivery ducts with relatively short length and very wide sectional area. It is understood in the context of the concept of some limiting conditions of E.M. Greitzer's B parameter. On the other hand, the A-boundary is a newly-found one. It tends to occur for narrow and long delivery ducts in the case of the suction duct with relatively short length.