In December 1997, the National Highway Traffic Safety Administration (NHTSA) sent an information request to nine automobile manufacturers requesting detailed technical information on the current industry practice on air bag technologies, and how air bag design and performance characteristics had evolved through the 1990s. The manufacturers provided the agency with the requested data, much of which was proprietary and confidential. The data included information on MY 1990 through MY 1998 vehicles. This report uses those data, as well as other available information, to illustrate the general trends in air bag design and performance characteristics. It also uses data from static and dynamic tests of various air bags and an assessment of air bag performance in terms of injury measures made on dummies representing occupants under low speed and high speed conditions. It also discusses the results of investigations of real world crashes by NHTSA's Special Crash Investigations office. The report is only intended to provide an overview of the trends in air bag characteristics and design changes. The limited analyses presented in this report are not intended to be a comprehensive report on the projected safety performance of the past, present, or future vehicle fleet.