Urban (re-)development projects may generate various positive and negative spatial externalities to employers. The assessment of such benefits is fraught with many methodological and empirical problems. This study aims to assess the order of magnitude of expected net benefits for incumbent employers that may accrue from a large-scale development project in the Zuidas area in the South-Western part of Amsterdam, the Netherlands. This development project is planned to transform the area into a large multifunctional urban agglomeration. We employ a specific stated preference method (namely, a willingness-to-pay method) to gauge the project's net socio-economic benefits for the current firms in the area concerned, paying special attention to the benefits associated with multifunctionality.