This paper develops and tests several models of pure Nash strategies of individuals who extract from a common pool resource when they are motivated by a combination of self-interest and other motivations such as altruism, reciprocity, inequity aversion and conformism. We test whether an econometric summary of subjects' strategies is consistent with one of these motivations using data from a series of common pool resource experiments conducted in three regions of Colombia. As expected, average extraction levels are less than that predicted by a model of pure self-interest, but are nevertheless sub-optimal. Moreover, we find that a model of conformism with monotonically increasing best response functions best describes average strategies. Our empirical results are inconsistent with models of altruism, reciprocity and inequity aversion.