In health care, cost sharing occurs when patients pay for a portion of health care costs not covered by health insurance. The "out-of-pocket" payment varies among healthcare plans and depends on whether or not the patient chooses to use a healthcare provider who is contracted with the healthcare plan's network. Examples of out-of-pocket payments involved in cost sharing include copays, deductibles, and coinsurance. A cost-sharing mechanism is a truthful mechanism for deciding what agents should be served by a public project, and how much each of them should pay.