In the United States, the company provides a monthly flat-fee for DVD and Blu-ray rentals. A subscriber creates a rental queue, a list, of films to rent. The films are delivered individually via the United States Postal Service from regional warehouses. As of March 28, 2011, Netflix had 58 shipping locations throughout the United States. The subscriber can keep the rented disc as long as desired, but there is a limit on the number of discs that each subscriber can have simultaneously via different tiers. To rent a new disc, the subscriber must return the previous disc in a metered reply mail envelope. Upon receipt, Netflix ships the next available disc in the subscriber's rental queue.