The realisation of cost-efficient Optical Burst Switching (OBS) networks can be greatly facilitated from minimising the number of contention resolution resources required at congested network nodes. In this paper we present a Fibre Delay Line (FDL) optimal allocation scheme where the total cost associated to the employment of FDLs is minimised subject to performance requirements defined in terms of maximum tolerable end-to-end blocking probability. The optimal buffer configuration is achieved by means of a constraint-handling genetic algorithm.We additionally increase the accuracy of our analysis by considering the non-Poissonian traffic characteristics of the OBS network under study. Results show that our method permits to identify an optimal FDL configuration that minimises the total buffer installation cost and simultaneously satisfies the network blocking probability requirements. Copyright © IARIA, 2012.