One of the main issues on the research agenda regarding stated preference methods concerns the heterogeneity of preferences either within or between individuals. We present a multilevel mixed model (MMM) to capture heterogeneity in deterministic utility components, instead of simply leaving them to random components. MMM captures heterogeneity at different levels individuals, locations, and groups of individuals sharing other characteristics. The results show that individuals' surroundings help to capture heterogeneity, and that can be controlled by specifying these aspects as predictors for this behavioral model. Therefore, MMM may contribute to the identification of the underlying structure affecting environmental decisions. (JEL D62, Q51). © 2014 by the Board of Regents of the University of Wisconsin System.