Publish/subscribe systems provide a useful paradigm for selective data dissemination and most of the complexity related to addressing and routing is encapsulated within the network infrastructure. The challenge of such systems is to organize the peers so as to best match the interests of the consumers, minimizing false positives and avoiding false negatives. In this paper, we propose and evaluate the use of R-trees for organizing the peers of a content-based routing network. We adapt three well-known variants of R-trees to the content dissemination problem striving to minimize the occurrence of false positives while avoiding false negatives. The effectiveness and accuracy of each structure is analyzed by extensive simulations.