The coefficient of restitution is an indicator of the elasticity of a collision. Restitution, or elastic rebound of a deformed surface, contributes to the change in velocity of collision partners, a common measure of injury severity in automobile collisions. Because of the complex nature of collisions between motor vehicles, the characterization of the expected magnitude of the coefficient in such collisions lacks detail and mechanisms influencing its value are not well understood. Using crash test data from the National Highway Traffic Safety Administration (NHTSA), this study investigates the expected magnitude of the coefficient of restitution and mechanisms influencing restitution in automobile collisions. Both vehicle-to-barrier and vehicle-to-vehicle tests are considered for all types of collisions. The influence of a variety of collision and vehicle parameters on restitution is also explored. Results show that impact velocity, through its relationship with vehicle crush, is highly influential in determining the magnitude of restitution. Restitution generally decreases as impact velocity increases. In full-frontal barrier collisions involving vehicles with certain engine configuration, however, a contradiction of the trend occurs as the coefficients value shifts upward before continuing to decrease with increasing velocity. Study of other parameters and collision types further clarifies restitution behavior.