Colorado Plains Medical Center did not respond to requests for comment.

In New York and Pennsylvania, private prices were less than two times the Medicare rates. Indiana, which has the highest private prices among the 25 states analyzed, pays roughly three times what Medicare does.

Many businesses that contract with insurance companies have no idea what their insurers are paying individual hospitals in their plan’s network. “We’ve never seen what was agreed upon,” said Jennifer Fairman, the benefits manager for people who work for Larimer County in Colorado. “We’ve been signing these blank checks.”

But soaring hospital costs have become a significant burden, and many businesses have off-loaded more of the expense onto their employees through higher premiums and deductibles. Families have struggled to cope with surprise medical bills and increasing out-of-pocket costs. The trend toward consolidation in the last several years has also spurred higher costs, as hospitals merged into bigger, more powerful systems that dominated their local markets, demanding ever-higher prices.

Unlike Medicare, which sets the price it will pay for a type of care, insurers often try to negotiate discounts with hospitals over charges, especially for outpatient services, said Chapin White, an adjunct senior policy researcher at RAND and one of the authors of the study.

The insurers don’t have a strong incentive to demand the lowest prices because many, working for employers that are self-insured, are “literally spending someone else’s money,” he said. Insurers are also frequently paid based on how much the employer spends; they take in more revenue when the employer spends more.

Insurers say they are motivated to keep hospital prices low and point to the battles they sometimes have over whether a high-priced system will be in their networks.