Does the hypothesis of preference for (group) efficiency account for subjects’ overcontribution in public good games or is this mostly noise? Using a bounded rational equilibrium approach, we aim at estimating the relative importance of effciency concerns relative to a noise argument. By using data from a VCM experiment with heterogeneous endowments and asymmetric information, we estimate a quantal response equilibrium (QRE) extension of a model in which subjects have preference for group efficiency. Under the hypothesis of homogeneous population most of the variability of contributions seems to be explained by noisy behaviors. A different picture emerges when we introduce cross-subject heterogeneity in concerns for group efficiency. In this case, the majority of the subjects makes contributions that are compatible with the hypothesis of preference for (group) efficiency. A formal likelihood-ratio test strongly rejects the models not allowing for noise in contributions and homogeneous subjects for the more general QRE extension with heterogeneous preferences for (group) efficiency coupled with noise in subjects’ behavior.(with Luca Corazzini)