Researchers have proposed that plug-in hybrid electric vehicles (PHEVs) performing vehicle-to-grid (V2G) ancillary services can accrue significant economic benefits without degrading vehicle performance. However, analyses to date have not evaluated the effect that automatic generator control signal energy content and call rate has on V2G ancillary service reliability and value. This research incorporates a new level of detail into the modeling of V2G ancillary services by incorporating probabilistic vehicle travel models, time-series automatic generation control signals, and time series ancillary services pricing into a non-linear dynamic simulation of the driving and charging behavior of PHEVs. Stochastic results are generated using Monte-Carlo methods. Results show that in order to integrate a V2G system into the existing market and power grid the V2G system will require: 1) an aggregative architecture to meet current industry standard reliability requirements; 2) the construction of low energy automatic generation control signals; 3) a lower percent call for V2G even if the pool of contracted ancillary service resources gets smaller; 4) a consideration of vehicle performance degradation due to the potential loss of electrically driven miles; and 5) a high-power home charging capability.