Individuals often benefit differently from cooperation. Using data from a laboratory experiment, I study contributions when subjects in a group differ in the benefit they get from a public good, in comparison with when they get a homogeneous return. In addition, I contrast the case where the return is certain with the case where it is subject to risk (uncertain). I investigate whether the effect of uncertainty differs when returns are ho- mogenous or heterogenous. I elicit both unconditional and conditional contribution behaviour to test if my results are robust to possible changes in subjects' beliefs regarding the contributions of others. I find that uncon- ditional contributions under uncertainty are lower than under certainty. Heterogeneity in returns also decreases unconditional contributions, but this effect is much weaker under uncertainty. Risk and heterogeneity do not affect conditional contributions.