Though the basic purpose of MPAs is marine ecosystem conservation, the question of their influence on the local economy is often critical since it governs their social acceptability. This paper addresses the problem of measuring the local economic impact of MPAs, on the basis of a comparative analysis of socio-economic field surveys of 14 case studies in Southern Europe. The surveys were performed in 2005 and 2006 within the framework of the EU funded multidisciplinary EMPAFISH research project. They cover a range of uses of ecosystem services related to the MPA: fishing (commercial and recreational), as well as non-extractive recreational activities (scuba-diving and snorkelling). More than 4,000 questionnaires were filled, providing information on behaviours and attitudes of users, as well as on the economic dimension of their activity. One of the issue is to separate the "reserve effect" from the "site effect".