This research investigates the impact of regulation on state automobile insurance markets while controlling for other state insurance market characteristics that may be related to performance. Data for a large sample of insurers are analyzed. The results suggest that insurers in competitive and non-stringently regulated states may benefit from market power by charging higher unit prices, however insurers in these states are on average more cost X-efficient and cost X-efficient insurers charge lower prices and earn smaller profits. The empirical results also suggest that insurers in some rate regulated states are less revenue and cost-scale efficient than in competitive states.