Insurers in states with the most concentrated markets have also been subject to the least oversight, according to a study ^[1] published by David Balto at the Center for American Progress, a left-leaning think tank.

State regulatory authorities haven’t brought any consumer protection suits against insurance companies in the last five years, according to Balto’s report, citing states such as Rhode Island, Alabama, Maine. According to this map ^[2] published today on CAP’s website, the top insurer controls 71% of the market in Rhode Island, 89% in Alabama, and 71% in Maine.

As Congress debates health care reform, Democrats have seized on a decades-old exemption from federal antitrust regulation that the insurance industry enjoys as one reason some insurers maintain near monopolies in individual states. While the merits of that argument are debatable ^[3], the CAP study asks whether states have the resources to enforce antitrust laws or if they are stretched too thin.

The study cites Georgetown health policy professor Karen Pollitz’s recent comments ^[4] to Congress: In four states, the Insurance Commissioner is also the fire marshal.

Sen Patrick Leahy (D-Vt.) used the study to reiterate his support for a repeal of the antitrust exemption for health and medical malpractice insurers. “If we remove it,they will have to compete,” Leahy said in a conference call today with reporters.

Leahy, along with Sen. Dianne Feinstein (D-Calif.)  and Senate Majority Leader Harry Reid (D-Nev.) plan to offer the repeal as an amendment to the health care bill.