This study looks at the potential reductions in hydrocarbons (HC) achievable through I/M of cars without catalytic converters. Reductions of 8% to 30 or 40% may be possible. The report is based on case studies of I/M programs being implemented in several states. The study identifies and analyzes factors which affect the cost and effectiveness of an I/M program. Effectiveness will be influenced by: the type of I/M test, frequency of inspection, the failure rate of inspected cars, the extent of deterioration of the emission rate between inspection, the quality of auto repair work, tampering cost varies with the type of tests, and the organizational structure, i.e., private or government run. The report also discusses certain critical factors which may determine a program's viability: Whether EPA has the authority to require I/M programs; the lack of technical data on auto performance and emissions; the public's willingness to accept the program; and state government's capacity to pay for implementing the program. Public acceptance is considered a major stumbling block. The report notes other factors which will affect the impact of an I/M program on air quality.