Millions of people with respiratory diseases have relied on oxygen equipment, delivered to their homes, to help them breathe. A basic setup, including three years of deliveries of small oxygen tanks, can be bought from pharmacies and other retailers for as little as $3,500, or about $100 a month.

Unless, that is, the buyer is Medicare, the government health care program for older Americans.

Despite enormous buying power, Medicare pays far more. Rather than buy oxygen equipment outright, Medicare rents it for 36 months before patients take ownership, and pays for a variety of services that critics say are often unnecessary.

The total cost to taxpayers and patients is as much as $8,280, or more than double what somebody might spend at a drugstore.

The high expense of oxygen equipment — which cost Medicare over $1.8 billion last year — is hardly an anomaly.