The research set out to determine whether the impact of widespread vehicle electronic immobilization for new cars in the United Kingdom from the mid-1990's can best be described in terms of the time-lag or reduced-pool theories. The time-lag theory suggests that the shape of the stolen vehicle curve results from the time it takes for methods of overcoming new security to be disseminated widely through the offending community. This assumes that regardless of the effectiveness of the latest vehicle security measures, with time it will be defeated. The reduced-pool theory suggests that new vehicle security will be effective on an incremental basis by reducing the rate of theft for each year of registration fitted with the new security technology. The testing of these theories in the United Kingdom was done by using data from the Home Office Car Theft Index to construct and analyze changes in the stolen vehicle age curve. The study found evidence that compulsory immobilization of vehicles by electronic means has been effective in reducing theft rates; however, there apparently has been some displacement of vehicle theft behavior toward both older and newer vehicles, although this was outweighed by overall gains in lower theft rates. The study recommends additional research based on disaggregate data rather than on the aggregate statistics used in this study. 5 figures and 22 notes