Two competing theories suggest different ways in which networks resolve collective action problems: small, dense networks enhance credible commitments supportive of cooperative solutions, while large boundary-spanning networks enhance search and information exchange supportive of coordinated solutions. Our empirical study develops and tests the competing credibility and search hypotheses in 22 estuary policy arenas, where fragmentation of authority creates collective problems and opportunities for joint gains through collaboration. The results indicate that search rather than credibility appears to pose the greater obstacle to collaboration; well-connected centrally located organizations engage in more collaborative activities than those embedded in small, dense networks.