We propose an approximate modelling method for analysing networks of optical burst switches with shared fibre delay lines (FDLs). To achieve a good accuracy in evaluating burst loss probabilities in the network, and allow a tractable solution method, a two-moment analysis is applied, both to traffic flows within network nodes and on network links. We believe the method is useful for evaluating the performance of share-per-node buffer architectures, which are generally more cost-efficient in terms of switching hardware requirements. Results show good accuracy compared to discrete-event simulations. © 2011 IEEE.