Contributions to public goods are premised on the expectation that the collective will realize benefit in excess of the value of the required contributions. However, past research has focused on public goods of fixed and known value, for which the added value of the produced public good is obvious. Research has largely ignored public goods whose eventual value is uncertain at the time contribution decisions must be made. When the distribution of possible outcomes creates the possibility of real loss, loss prospects can directly discourage contributions because of loss aversion, and loss prospects can indirectly discourage contributions by fueling fears that others will not contribute. This paper details two empirical investigations exploring the effects of outcome variance on both individuals' contributions to a public good and their reasons for contributing. Results show that contributions to a public good are negatively affected by the prospect of losses in the distribution of possible outcomes. Implications of these findings for social dilemma research and the effective management of collective action are discussed.