I’ve spent more than a decade writing about the American health care system, looking at what doesn’t work for patients and at legislators’ plans to fix it. Lately, I’ve become really interested in ambulance billing, an area of the health system that has received less scrutiny from politicians, but is a frequent source of surprising and unpredictable bills.

Here’s why: The ambulance industry is in the middle of rapid change, as cities and counties increasingly outsource their emergency response services to privately owned companies. Ambulances are becoming a significant source of surprise medical bills. They are more than twice as likely to be out of network with health insurers as emergency room doctors. As one health economist recently told me, “If you call 911 for an ambulance, it’s basically a coin flip whether or not that ambulance will be in or out of network.”

All of this can leave patients with large surprise medical bills, and I want to better understand what that experience is like. If you’ve taken an ambulance ride in the past five years, I would love to hear from you — especially if you still have any related billing documents. I’m interested in learning about both the quality of care you received (how quickly the ambulance came, for example) and the billing experience.