A number of midsize four-door passenger cars equipped with air bags were crashed at 40 mi/h (64 km/h) into a deformable barrier with an overlap of 40 percent of the vehicle Width. An instrumented Hybrid III 50th percentile male dummy was positioned in the driver' seat with the seat belt fastened. In nearly all these crashes, the air bag and seat belt protected the driver dummy from sustaining loads to the head that would exceed injury thresholds specified by U.S. federal motor vehicle safety standards. However, in several crashes, as the vehicle rebounded and rotated from the barrier, the dummy experienced considerable lateral motion relative to the occupant compartment. This motion suggests that the mostly good upper body injury results may not adequately indicate the risks for Occupants of different stature and/0r occupants not seated as specified in the Federal Motor Vehicle Safety Standard 208 procedures. High speed film analysis and postcrash vehicle inspection suggest that occupant compartment deformation plays an important role in the performance of the restraint system in many offset frontal crashes. The air bag, seat belt, driver door, and the seat itself are each important components in controlling occupant kinematics as the vehicle rebounds and rotates from an offset frontal crash.