In multicluster systems, and more generally, in grids, parallel applications may require co-allocation, i.e., the simultaneous allocation of resources such as processors in multiple clusters. Although co-allocation enables the allocation of more processors than available on a single cluster, depending on the applications? communication characteristics, it has the potential disadvantage of increased execution times due to relatively slow wide-area communication. In this paper, we present two job placement policies, the Cluster Minimization and the Flexible Cluster Minimization policies which take into account the wide-area communication overhead when co-allocating applications across the clusters. We have implemented these policies in our grid scheduler called KOALA in order to serve different job request types. To assess the performance of the policies, we perform experiments in a real multicluster testbed using communication-intensive parallel applications.