The expected energy exchange between cooperating systems is an important information supporting capacity expansion planning for electric power systems. A model based on engineering considerations and a program system on IBM/PC-XT or AT compatibles has been developed for the stochastic analysis of the electric energy exchange between two interconnected power systems. Data required for the analysis are expected generation and load in the individual systems, and interties data. This work has been carried out in the frame of the IIASA Contracted Study "Modeling of interconnected power systems".