As the share of intermittent renewable energy sources increases, it will be necessary to increase the volume of frequency regulation reserves. New sources of reserves can be found in the distributed energy resources (controllable loads, Electrical Vehicles (EVs), distributed generation units). However, it is necessary to adapt the frequency-regulation market-design in order to allow the participation of these new resources through new market actors called “aggregators”. The aim of this article is to provide a modular framework to analyze these frequency regulation markets or mechanisms, to i) make a benchmark of four major European System Operators; ii) to identify barriers to entry for aggregators and iii) to identify some best practices.