In the past, many researchers have used stochastic streamflow models along with sequent peak algorithm or simulation to obtain storage-reliability-yield (S-R-Y) relationships for a reservoir. These S-R-Y relationships consider only the probability of failure, but not the likely consequences of the failure (vulnerability). In this paper, separate contours of reservoir performance, namely reliability and vulnerability (event-based), have been developed on the storage-yield plane, using stochastic reservoir simulation. These contours of performance, when superposed, give rise to the storage-performance-yield (S-P-Y) relationships, the construction of which is illustrated in this paper through a case example. These relationships provide more comprehensive information to the reservoir planner regarding performance than the S-R-Y relationships. © 1995 Journals Oxford Ltd