A reliable dynamic measure to predict vehicle rollover under various conditions must be developed in order to quantitatively analyze the rollover propensities of vehicles. Several efforts have been made and are introduced in this paper on the development of such a dynamic measure of vehicle rollover stability.The position of the axis about which a vehicle rolls over (rollover axis) must be determined prior to developing a vehicle rollover propensity measure. For this reason, an investigation into the central axis concept was first performed. However, as shown in the paper, the unpredictability of the central axis position of the vehicle leads to the analyses of three other possible rollover axes. Investigations into the kinetic and potential energies of the vehicle system and its components have resulted in the modification and the extension of a previously developed energy based function called Rollover Prevention Energy Reserve (RPER).The RPER function is defined as the difference between the energy needed to bring the vehicle to its tip-over position and the vehicle rotational kinetic energy which can be transferred into gravitational potential energy to lift the vehicle. According to this definition, the value of the RPER function drops below zero before a vehicle reaches its tip-over position in a rollover case, but always remains positive in a non-rollover case. The algorithm developed to calculate RPER is presented in the paper.The RPER function has been validated using experimental results obtained from full-scale vehicle testing performed by the University of Missouri-Columbia. Six light trucks, vans, and utility vehicles, as well as two passenger cars, were extensively tested in a variety of handling and rollover maneuvers. Different roadside geometries, including transitions from pavement onto soil and into a curb, were used. The validation plots present the RPER functions for both rollover and non-rollover cases.