The present article argues that bargaining over how the gains from cooperation in the WTO should be shared between governments constitutes a major obstacle to multilateral liberalization. Since each government is uncertain about how other governments evaluate possible WTO agreements and their best alternatives to a negotiated agreement, it has an incentive to engage in aggressive gain claiming, hoping to shape the resulting agreement in its own favor. However, aggressive gain claiming may result in delay and reduced ambition of an agreement, it may damage states' systemic interest in the effective and stable functioning of the WTO, and it may provoke peer pressure. How governments frame these benefits and costs and how they coordinate their negotiating positions in bargaining coalitions also shapes their gain claiming strategies. The hypotheses about the determinants of gain claiming submitted in this article are based on a series of interviews conducted with members of national delegations and WTO employees, as well as on a survey of national delegations.