An increasing number of researchers have hypothesized that regulatory attempts to improve automotive safety through product design would be at least partially offset by driver behavioral changes. This article analyzes two independent data sets to test whether differences in driver behavior exist between cars equipped with air bags and those not so equipped. An analysis of an insurance industry generated data set reveals that relative injury claims increase following adoption of an air bag system. Since there is no indication that the increase diminishes over time, the results appear to be attributable to offsetting behavior as opposed to a sorting of auto buyers. Analyses of 1993 Virginia State Police accident reports indicate that air-bag-equipped cars tend to be driven more aggressively and that aggressiveness appears to offset the effect of the air bag for the driver and increases the risk of death to others. Copyright 1995 by the University of Chicago.