People waiting for transplants are listed at their local transplant center and on a national waiting list maintained by the United Network for Organ Sharing (UNOS). UNOS is responsible for overseeing organ placement and providing fair and equitable placement of donated organs. When an organ becomes available, several factors are taken into consideration. These factors include blood and tissue type and size of the donor and transplant candidate and the candidate’s medical condition, time spent on the waiting list, and urgency of need. Geographic location is also a factor, as timing is critical and transportation times must be kept to a minimum.