The most common result in public good games (PGG) is that uncertainty about the returns of the good leads to a decrease in contributions. We aim to provide further evidence of this effect, and explore whether it could be driven by the plausible deniability about one’s selfishness that risk offers: a justification for yourself that the risk made contributing futile, and/or towards others that you contributed but were negatively affected by risk. We explore this by varying whether the returns from the PGG are certain or risky, and whether participants can hide behind risk to justify their free-riding. We find no statistically significant difference between contributions in the certain and risky treatments. Although a reduction in contributions under risk is more prevalent, a substantial fraction of the existing studies in this area find results in line with ours. We also found no difference between our two risky treatments, suggesting that excuses did not lead to changes in contributions. In line with results in lying and cheating studies, we find that plausible deniability is not exploited when it would justify a big departure from prosocial behaviour. The extent to which effects of plausible deniability extend to contexts other than allocation tasks (as in the seminal moral wiggle room study by Dana et al, 2007) has received considerable attention in the literature and here we offer some evidence of a limited effect in the context of public good contributions.