This paper provides a method to infer the presence of treatment spillovers within markets where a fraction of agents is treated. We model individual outcomes as functions of the assigned treatment status and the distribution of assigned treatments in a market. We develop a two-step identification and estimation method, focusing first on the treatment distribution among individuals within markets and then on the treatment distribution across markets. We apply our approach to training programs for unemployed individuals in France using rich administrative data. Our results provide evidence of interactions within local labor markets as potential individual outcomes vary with the proportion of treated individuals.