We investigate the effect of intragroup competition and risky marginal per capita returns on subjects' cooperative behavior in a one-shot public good game – following the wellknown approach proposed by Fischbacher, Gächter, and Fehr (2001) and extending the Colasante et al. (2019) and Colasante et al. (2018) parametrization. We are aiming to study the interaction between environment and social preferences and test the existence of a causal relationship of risk and competition over cooperative behavior when an individual’s benefit of the public good is heterogeneous and uncertain. Our results report experimental evidence about competition fostering cooperative behavior leading a raise contribution for all the subjects regardless of their soc...