A key issue to ensuring power system stability is the ability to balance power generation and demand. Real-time balancing is achieved through automatic frequency regulation: primary and secondary controls. Electric vehicles with their storage capacities could be an opportunity to achieve this balance. As electric vehicles (EVs) are principally dedicated to short trips (mainly between home and office), their daily time of use is quite small (less than 2 hours). EVs could be plugged in to the power network more than 20 hours per day. This duration is longer than the time required to fully charge their batteries. A real opportunity consequently exists for grid support through frequency regulation. In the present paper, we propose an economic evaluation of revenues from primary frequency regulation for an aggregator managing an EV fleet. Our study is based on French data for tariffs for capacity reserve, daily trips, electricity prices and tariffs.