This paper presents a single-moment method for determining the node-to-node grades of service of a circuit-switched communication network employing a routing strategy called "originating-office control with spill-forward." An example of such a network is the European AUTOVON. The new method makes use of the concept of "path-loss sequence" and the techniques in system reliability analysis to determine the probability of each route being used to complete a call. Results from a digital computer implementation of the method and comparisons with other methods are discussed.