Some of the health care legislation being considered by Congress would require insurers to increase their disclosure to patients of possible out-of-network costs. And President Obama has proposed changing how Medicare sets its payments to doctors and hospitals. But there are no specific proposals to control prices for out-of-network medical services.

In the survey, patients were insured but saw doctors who were out of their networks of care providers. Those doctors have no obligation to accept the out-of-network fee from insurers as payment in full. Patients may then be accountable for the balance.

“That is what generally happens,” said Susan Pisano, a spokeswoman for the health insurers’ group. “The consumer is responsible.”

The survey looked at 10 companies that insure patients in the 30 most populous states; the companies provided some of the highest bills from 2008. Researchers excluded two types of charges that were likely to be erroneous: those that were greater than 10,000 percent of Medicare’s fees for a procedure, or more than 2,000 percent of Medicare’s fees and also more than 50 percent higher than the next-highest bill for the same procedure.

Image Ryan Davis and his mother, Maria, at their Miller Place home. The family was billed $6,000 for three stitches he received under his lower lip at the local hospital's emergency room. Credit... Maxine Hicks for The New York Times

State laws protecting patients from getting stuck with medical bills in excess of their normal deductibles or co-payments vary widely, said Betsy M. Pelovitz, the group’s vice president for state policy. And, she said, the laws often offer little or no protection to patients who seek care outside their insurance networks.

In New York, patients with managed-care insurers cannot be asked to pay more than the applicable co-payment, deductible or co-insurance for an ambulance regardless of whether the provider is in or out of their network. In New Jersey, hospital emergency rooms treating Medicaid managed-care patients must accept Medicaid payments as payment in full and cannot bill patients extra. In Connecticut, a state law says it is “unfair trade practice” for medical providers to ask patients to pay more than a deductible or co-payment for services covered by their insurance.