Business services show a strong trend towards spatial concentration. In this paper we propose a method to estimate the causes of such a behaviour. We choose six different explanations, from amongst the ones proposed by theory and partial empirical studies, and include them together in a simple econometric model. We apply this model to data for the region of Aragon, a case of particular interest for the study of geographical concentration because of the disproportionate weight of the capitals share on regional economic activity, an issue which must be dealt with when interpreting the estimated coefficients. Our results show that scale and agglomeration economies are the main influences in location decisions.