If you think costs would come down if hospitals were all owned and operated by big for-profit corporations like Hospital Corporation of America, you might want to take a look at a study published last week by the journal Health Affairs.

Of the 50 U.S. hospitals that mark up prices the most, 49 of them are part of for-profit hospital chains, according to the study’s authors, Ge Bai of Washington & Lee University and Gerard Anderson of the Johns Hopkins Bloomberg School of Public Health.

Using 2012 data provided by 4,483 hospitals to the Centers for Medicare and Medicaid Services, Bai and Anderson found that those 50 had an average markup of 1,013 percent over what Medicare pays for the thousands of items on hospitals’ “chargemasters.” (Chargemasters are lists of all the items and services hospitals bill for. Hospitals set their own charges. Few states set any limits on what hospitals can charge.) That’s almost three times the average markup at the other 4,433 hospitals. The average markup for all those other hospitals—most of them nonprofits—was 340 percent.

Of those high-markup 50, more than a fourth of them are owned and operated by Nashville-based Hospital Corporation of America (HCA). But with 14 hospitals on the list, HCA was just in second place. A full half of the top 50 are owned by HCA’s biggest rival, Community Health Systems, a Franklin, Tennessee company that operates 199 hospitals in 29 states.

At the very top of the markup list was North Okaloosa Medical Center in Crestview, Florida. That hospital, in the Sunshine State’s panhandle, had the distinction of marking up its costs an average of 1260 percent. The Atlantic’s Olga Khazan took a look at North Okaloosa’s markups. She found, for example, that the hospital charged $79,350 to treat a hemorrhage. That’s compared to Medicare’s reimbursement of $5,177.