The objective of this paper is to present a mechanism to determine the two-way energy storage capacity of a large pool of electric vehicles (EV) which can be contracted in ancillary services market on a long-term basis to provide the regulation up (RU) and regulation down (RD) to the grid. The proposed mechanism uses a scheme which delivers the schedule of power supplied to or drawn from the grid by treating the mobility attributes dependent electrical parameters. Two operational places, the workplace, and the home were identified as per driving pattern of customers for the provision of regulation ancillary service. An illustrative model considering a fleet of representative battery electric vehicle (BEV) is presented based on the mechanism, to obtain the minute-wise storage capacity that can be contracted in the market to provide frequency regulation to the grid. Results demonstrate that two major mobility traits namely, driven distance and arrival pattern, as well as the charging and discharging power standards directly influences the regulation schedule. Further, it has been realized that even though the charging cost is associated with energy consumption, the regulation provision will yield a notable revenue stream on a long-term capacity commitment basis. This supplements the concept of EVs participation in power markets by virtue of their high ramp up ramp down speed capabilities.