Spurring the creation of accountable care organizations (ACOs) was a signature initiative in the Patient Protection and Affordable Care Act of 2010 (PPACA). To achieve potential efficiencies by having health care delivery coordinated by multiple health care entities (eg, hospitals, physician groups, clinics, health care systems), the act invites such entities to integrate in ACOs and instructs the Medicare program to share with an ACO any cost savings it can demonstrate.1 Observers are expressing concern, however, that newly established ACOs are joining health care organizations that otherwise would compete with each other, thus creating networks with dangerous market power.2 It appears that the main purpose of health care entities in forming ACOs may not be to achieve cost savings to be shared with Medicare but to strengthen negotiating power over purchasers in the private sector.