We study a finitely repeated public goods game (based on the voluntary contribution mechanism) played under complete uncertainty about the marginal benefit of the public good relative to the private consumption (commonly known as the marginal per capita return): neither one's marginal per capita return nor other players' marginal per capita returns are known at the time of decisionmaking. We show that contributions are equivalent when the rate of return is predetermined and when it is uncertain, and display a similar decay over time. Combined with the previous experimental findings, our results suggest that the cooperation in public goods games is sensitive to the source of uncertainty about marginal per capita return.