Publish-subscribe systems are evolving toward using content-based subscription rather than subject-based subscription. A key problem in implementing such systems is that a straightforward mapping from matching sets to multicast groups produces a number of groups that rapidly grows beyond practical limits. This paper proposes a set of alternative algorithms for solving this problem, by: (1) using a smaller set of overbroad multicast groups, judiciously chosen to minimize imprecision; (2) issuing multiple multicasts to appropriately chosen clusters; or (3) sending an event over multiple hops each involving a multicast to a set of neighbors. We evaluate these algorithms on a simulated wide-area network. We find that (1) a simple flooding algorithm is viable over an extensive range of conditions; and (2) under conditions of high selectivity and high regionalism of subscriptions, the other approaches mentioned above perform significantly better; however, the specific algorithm to use depends upon the economics of deployment.